神马文学网XML Schema Part 1: Structures
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XML Schema Part 1: StructuresW3C Recommendation 2 May 2001
This version:http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/
(inXML (with its ownDTD,XSL stylesheet) andHTML), with separate provision of theschema andDTD for schemas described herein.Latest version:http://www.w3.org/TR/xmlschema-1/
Previous version:http://www.w3.org/TR/2001/PR-xmlschema-1-20010330/
Editors:Henry S. Thompson (University of Edinburgh)
David Beech (Oracle Corporation)
Murray Maloney (for Commerce One)
Noah Mendelsohn (Lotus Development Corporation)
Copyright ©2001W3C® (MIT,INRIA,Keio), All Rights Reserved. W3Cliability,trademark,document use andsoftware licensing rules apply.
XML Schema: Structures specifies the XML Schema definition language, which offers facilities for describing the structure and constraining the contents of XML 1.0 documents, including those which exploit the XML Namespace facility. The schema language, which is itself represented in XML 1.0 and uses namespaces, substantially reconstructs and considerably extends the capabilities found in XML 1.0 document type definitions (DTDs). This specification depends on XML Schema Part 2: Datatypes.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. The latest status of this document series is maintained at the W3C.
This document has been reviewed by W3C Members and other interested parties and has been endorsed by the Director as a W3C Recommendation. It is a stable document and may be used as reference material or cited as a normative reference from another document. W3C‘s role in making the Recommendation is to draw attention to the specification and to promote its widespread deployment. This enhances the functionality and interoperability of the Web.
This document has been produced by theW3C XML Schema Working Group as part of the W3CXML Activity. The goals of the XML Schema language are discussed in theXML Schema Requirements document. The authors of this document are the XML Schema WG members. Different parts of this specification have different editors.
This version of this document incorporates some editorial changes from earlier versions.
Please report errors in this document towww-xml-schema-comments@w3.org (archive). The list of known errors in this specification is available athttp://www.w3.org/2001/05/xmlschema-errata.
The English version of this specification is the only normative version. Information about translations of this document is available athttp://www.w3.org/2001/05/xmlschema-translations.
A list of current W3C Recommendations and other technical documents can be found athttp://www.w3.org/TR/.
1Introduction
1.1Purpose
1.2Dependencies on Other Specifications
1.3Documentation Conventions and Terminology
2Conceptual Framework
2.1Overview of XML Schema
2.2XML Schema Abstract Data Model
2.3Constraints and Validation Rules
2.4Conformance
2.5Names and Symbol Spaces
2.6Schema-Related Markup in Documents Being Validated
2.7Representation of Schemas on the World Wide Web
3Schema Component Details
3.1Introduction
3.2Attribute Declarations
3.3Element Declarations
3.4Complex Type Definitions
3.5AttributeUses
3.6Attribute Group Definitions
3.7Model Group Definitions
3.8Model Groups
3.9Particles
3.10Wildcards
3.11Identity-constraint Definitions
3.12Notation Declarations
3.13Annotations
3.14Simple Type Definitions
3.15Schemas as a Whole
4Schemas and Namespaces: Access and Composition
4.1Layer 1: Summary of the Schema-validity Assessment Core
4.2Layer 2: Schema Documents, Namespaces and Composition
4.3Layer 3: Schema Document Access and Web-interoperability
5Schemas and Schema-validity Assessment
5.1Errors in Schema Construction and Structure
5.2Assessing Schema-Validity
5.3Missing Sub-components
5.4Responsibilities of Schema-aware Processors
Appendices
ASchema for Schemas (normative)
BReferences (normative)
COutcome Tabulations (normative)
DRequired Information Set Items and Properties (normative)
ESchema Components Diagram (non-normative)
FGlossary (non-normative)
GDTD for Schemas (non-normative)
HAnalysis of the Unique Particle Attribution Constraint (non-normative)
IReferences (non-normative)
JAcknowledgements (non-normative)
1 Introduction
This document sets out the structural part (XML Schema: Structures) of the XML Schema definition language.
Chapter 2 presents aConceptual Framework (§2) for XML Schemas, including an introduction to the nature of XML Schemas and an introduction to the XML Schema abstract data model, along with other terminology used throughout this document.
Chapter 3,Schema Component Details (§3), specifies the precise semantics of each component of the abstract model, the representation of each component in XML, with reference to a DTD and XML Schema for an XML Schema document type, along with a detailed mapping between the elements and attribute vocabulary of this representation and the components and properties of the abstract model.
Chapter 4 presentsSchemas and Namespaces: Access and Composition (§4), including the connection between documents and schemas, the import, inclusion and redefinition of declarations and definitions and the foundations of schema-validity assessment.
Chapter 5 discussesSchemas and Schema-validity Assessment (§5), including the overall approach to schema-validity assessment of documents, and responsibilities of schema-aware processors.
The normative appendices include aSchema for Schemas (normative) (§A) for the XML representation of schemas andReferences (normative) (§B).
The non-normative appendices include theDTD for Schemas (non-normative) (§G) and aGlossary (non-normative) (§F).
This document is primarily intended as a language definition reference. As such, although it contains a few examples, it is not primarily designed to serve as a motivating introduction to the design and its features, or as a tutorial for new users. Rather it presents a careful and fully explicit definition of that design, suitable for guiding implementations. For those in search of a step-by-step introduction to the design, the non-normative[XML Schema: Primer] is a much better starting point than this document.
1.1 PurposeThe purpose of XML Schema: Structures is to define the nature of XML schemas and their component parts, provide an inventory of XML markup constructs with which to represent schemas, and define the application of schemas to XML documents.
The purpose of an XML Schema: Structures schema is to define and describe a class of XML documents by using schema components to constrain and document the meaning, usage and relationships of their constituent parts: datatypes, elements and their content and attributes and their values. Schemas may also provide for the specification of additional document information, such as normalization and defaulting of attribute and element values. Schemas have facilities for self-documentation. Thus, XML Schema: Structures can be used to define, describe and catalogue XML vocabularies for classes of XML documents.
Any application that consumes well-formed XML can use the XML Schema: Structures formalism to express syntactic, structural and value constraints applicable to its document instances. The XML Schema: Structures formalism allows a useful level of constraint checking to be described and implemented for a wide spectrum of XML applications. However, the language defined by this specification does not attempt to provide all the facilities that might be needed by any application. Some applications may require constraint capabilities not expressible in this language, and so may need to perform their own additional validations.
1.2 Dependencies on Other SpecificationsThe definition of XML Schema: Structures depends on the following specifications:[XML-Infoset],[XML-Namespaces],[XPath], and[XML Schemas: Datatypes].
SeeRequired Information Set Items and Properties (normative) (§D) for a tabulation of the information items and properties specified in[XML-Infoset] which this specification requires as a precondition to schema-aware processing.
1.3 Documentation Conventions and TerminologyThe section introduces the highlighting and typography as used in this document to present technical material.
Special terms are defined at their point of introduction in the text. For example a term is something used with a special meaning. The definition is labeled as such and the term it defines is displayed in boldface. The end of the definition is not specially marked in the displayed or printed text. Uses of defined terms are links to their definitions, set off with middle dots, for instance·term·.
Non-normative examples are set off in boxes and accompanied by a brief explanation:
Example
And an explanation of the example.
The definition of each kind of schema component consists of a list of its properties and their contents, followed by descriptions of the semantics of the properties:
Schema Component: Example
Definition of the property.
References to properties of schema components are links to the relevant definition as exemplified above, set off with curly braces, for instance{example property}.
The correspondence between an element information item which is part of the XML representation of a schema and one or more schema components is presented in a tableau which illustrates the element information item(s) involved. This is followed by a tabulation of the correspondence between properties of the component and properties of the information item. Where context may determine which of several different components may arise, several tabulations, one per context, are given. The property correspondences are normative, as are the illustrations of the XML representation element information items.
In the XML representation, bold-face attribute names (e.g. count below) indicate a required attribute information item, and the rest are optional. Where an attribute information item has an enumerated type definition, the values are shown separated by vertical bars, as for size below; if there is a default value, it is shown following a colon. Where an attribute information item has a built-in simple type definition defined in[XML Schemas: Datatypes], a hyperlink to its definition therein is given.
The allowed content of the information item is shown as a grammar fragment, using the Kleene operators ?, * and +. Each element name therein is a hyperlink to its own illustration.
NOTE: The illustrations are derived automatically from theSchema for Schemas (normative) (§A). In the case of apparent conflict, theSchema for Schemas (normative) (§A) takes precedence, as it, together with the·Schema Representation Constraints·, provide the normative statement of the form of XML representations. XML Representation Summary: example Element Information Item
count =integer
size = (large | medium | small) : medium>
Content: (all |any*)
Example Schema Component
Property Representation
{example property} Description of what the property corresponds to, e.g. the value of the size[attribute]
References to elements in the text are links to the relevant illustration as exemplified above, set off with angle brackets, for instance
References to properties of information items as defined in[XML-Infoset] are notated as links to the relevant section thereof, set off with square brackets, for example[children].
Properties which this specification defines for information items are introduced as follows:
PSVI Contributions for example information items
The value the property gets.
References to properties of information items defined in this specification are notated as links to their introduction as exemplified above, set off with square brackets, for example[new property].
The following highlighting is used for non-normative commentary in this document:
NOTE: General comments directed to all readers.
Following[XML 1.0 (Second Edition)], within normative prose in this specification, the words may and must are defined as follows:
mayConforming documents and XML Schema-aware processors are permitted to but need not behave as described.mustConforming documents and XML Schema-aware processors are required to behave as described; otherwise they are in error.
Note however that this specification provides a definition of error and of conformant processors‘ responsibilities with respect to errors (seeSchemas and Schema-validity Assessment (§5)) which is considerably more complex than that of[XML 1.0 (Second Edition)].
2 Conceptual Framework
This chapter gives an overview of XML Schema: Structures at the level of its abstract data model.Schema Component Details (§3) provides details on this model, including a normative representation in XML for the components of the model. Readers interested primarily in learning to write schema documents may wish to first read[XML Schema: Primer] for a tutorial introduction, and only then consult the sub-sections ofSchema Component Details (§3) named XML Representation of ... for the details.
2.1 Overview of XML SchemaAn XML Schema consists of components such as type definitions and element declarations. These can be used to assess the validity of well-formed element and attribute information items (as defined in[XML-Infoset]), and furthermore may specify augmentations to those items and their descendants. This augmentation makes explicit information which may have been implicit in the original document, such as normalized and/or default values for attributes and elements and the types of element and attribute information items.
Schema-validity assessment has two aspects:
1determining local schema-validity, that is whether an element or attribute information item satisfies the constraints embodied in the relevant components of an XML Schema;
2 Synthesizing an overall validation outcome for the item, combining local schema-validity with the results of schema-validity assessments of its descendants, if any, and adding appropriate augmentations to the infoset to record this outcome.
Throughout this specification, the word valid and its derivatives are used to refer to clause1 above, the determination of local schema-validity.
Throughout this specification, the word assessment is used to refer to the overall process of local validation, schema-validity assessment and infoset augmentation.
2.2 XML Schema Abstract Data Model2.2.1Type Definition Components
2.2.2Declaration Components
2.2.3Model Group Components
2.2.4Identity-constraint Definition Components
2.2.5Group Definition Components
2.2.6Annotation Components
This specification builds on[XML 1.0 (Second Edition)] and[XML-Namespaces]. The concepts and definitions used herein regarding XML are framed at the abstract level ofinformation items as defined in[XML-Infoset]. By definition, this use of the infoset provides a priori guarantees ofwell-formedness (as defined in[XML 1.0 (Second Edition)]) andnamespace conformance (as defined in[XML-Namespaces]) for all candidates for·assessment· and for all·schema documents·.
Just as[XML 1.0 (Second Edition)] and[XML-Namespaces] can be described in terms of information items, XML Schemas can be described in terms of an abstract data model. In defining XML Schemas in terms of an abstract data model, this specification rigorously specifies the information which must be available to a conforming XML Schema processor. The abstract model for schemas is conceptual only, and does not mandate any particular implementation or representation of this information. To facilitate interoperation and sharing of schema information, a normative XML interchange format for schemas is provided.
Schema component is the generic term for the building blocks that comprise the abstract data model of the schema. An XML Schema is a set of·schema components·. There are 13 kinds of component in all, falling into three groups. The primary components, which may (type definitions) or must (element and attribute declarations) have names are as follows:
Simple type definitions Complex type definitions Attribute declarations Element declarations
The secondary components, which must have names, are as follows:
Attribute group definitions Identity-constraint definitions Model group definitions Notation declarations
Finally, the "helper" components provide small parts of other components; they are not independent of their context:
Annotations Model groups Particles Wildcards Attribute Uses
During·validation·, declaration components are associated by (qualified) name to information items being·validated·.
On the other hand, definition components define internal schema components that can be used in other schema components.
Declarations and definitions may have and be identified by names, which are NCNames as defined by[XML-Namespaces].
Several kinds of component have a target namespace, which is either·absent· or a namespace name, also as defined by[XML-Namespaces]. The·target namespace· serves to identify the namespace within which the association between the component and its name exists. In the case of declarations, this in turn determines the namespace name of, for example, the element information items it may·validate·.
NOTE: At the abstract level, there is no requirement that the components of a schema share a·target namespace·. Any schema for use in·assessment· of documents containing names from more than one namespace will of necessity include components with different·target namespaces·. This contrasts with the situation at the level of the XML representation of components, in which each schema document contributes definitions and declarations to a single target namespace.
·Validation·, defined in detail inSchema Component Details (§3), is a relation between information items and schema components. For example, an attribute information item may·validate· with respect to an attribute declaration, a list of element information items may·validate· with respect to a content model, and so on. The following sections briefly introduce the kinds of components in the schema abstract data model, other major features of the abstract model, and how they contribute to·validation·.
2.2.1 Type Definition Components
The abstract model provides two kinds of type definition component: simple and complex.
This specification uses the phrase type definition in cases where no distinction need be made between simple and complex types.
Type definitions form a hierarchy with a single root. The subsections below first describe characteristics of that hierarchy, then provide an introduction to simple and complex type definitions themselves.
2.2.1.1 Type Definition Hierarchy
Except for a distinguished·ur-type definition·, every·type definition· is, by construction, either a·restriction· or an·extension· of some other type definition. The graph of these relationships forms a tree known as the Type Definition Hierarchy.
A type definition whose declarations or facets are in a one-to-one relation with those of another specified type definition, with each in turn restricting the possibilities of the one it corresponds to, is said to be a restriction. The specific restrictions might include narrowed ranges or reduced alternatives. Members of a type, A, whose definition is a·restriction· of the definition of another type, B, are always members of type B as well.
A complex type definition which allows element or attribute content in addition to that allowed by another specified type definition is said to be an extension.
A distinguished ur-type definition is present in each·XML Schema·, serving as the root of the type definition hierarchy for that schema. The ur-type definition, whose name is anyType, has the unique characteristic that it can function as a complex or a simple type definition, according to context. Specifically,·restrictions· of the ur-type definition can themselves be either simple or complex type definitions.
A type definition used as the basis for an·extension· or·restriction· is known as the base type definition of that definition.
2.2.1.2 Simple Type Definition
A simple type definition is a set of constraints on strings and information about the values they encode, applicable to the·normalized value· of an attribute information item or of an element information item with no element children. Informally, it applies to the values of attributes and the text-only content of elements.
Each simple type definition, whether built-in (that is, defined in[XML Schemas: Datatypes]) or user-defined, is a·restriction· of some particular simple·base type definition·. For the built-in primitive types, this is the simple version of the·ur-type definition·, whose name is anySimpleType. This is in turn understood to be a restriction of the·ur-type definition·. Simple types may also be defined whose members are lists of items themselves constrained by some other simple type definition, or whose membership is the union of the memberships of some other simple type definitions. List and union simple type definitions are also understood as restrictions of the simple·ur-type definition·.
For detailed information on simple type definitions, seeSimple Type Definitions (§3.14) and[XML Schemas: Datatypes]. The latter also defines an extensive inventory of pre-defined simple types.
2.2.1.3 Complex Type Definition
A complex type definition is a set of attribute declarations and a content type, applicable to the[attributes] and[children] of an element information item respectively. The content type may require the[children] to contain neither element nor character information items (that is, to be empty), to be a string which belongs to a particular simple type or to contain a sequence of element information items which conforms to a particular model group, with or without character information items as well.
Each complex type definition is either
a restriction of a complex·base type definition·
or
an·extension· of a simple or complex·base type definition·
or
a·restriction· of the·ur-type definition·.
A complex type which extends another does so by having additional content model particles at the end of the other definition‘s content model, or by having additional attribute declarations, or both.
NOTE: This specification allows only appending, and not other kinds of extensions. This decision simplifies application processing required to cast instances from derived to base type. Future versions may allow more kinds of extension, requiring more complex transformations to effect casting.
For detailed information on complex type definitions, seeComplex Type Definitions (§3.4).
2.2.2 Declaration Components
There are three kinds of declaration component: element, attribute, and notation. Each is described in a section below. Also included is a discussion of element substitution groups, which is a feature provided in conjunction with element declarations.
2.2.2.1 Element Declaration
An element declaration is an association of a name with a type definition, either simple or complex, an (optional) default value and a (possibly empty) set of identity-constraint definitions. The association is either global or scoped to a containing complex type definition. A top-level element declaration with name ‘A‘ is broadly comparable to a pair of DTD declarations as follows, where the associated type definition fills in the ellipses:
Element declarations contribute to·validation· as part of model group·validation·, when their defaults and type components are checked against an element information item with a matching name and namespace, and by triggering identity-constraint definition·validation·.
For detailed information on element declarations, seeElement Declarations (§3.3).
2.2.2.2 Element Substitution Group
In XML 1.0, the name and content of an element must correspond exactly to the element type referenced in the corresponding content model.
Through the new mechanism of element substitution groups, XML Schemas provides a more powerful model supporting substitution of one named element for another. Any top-level element declaration can serve as the defining element, or head, for an element substitution group. Other top-level element declarations, regardless of target namespace, can be designated as members of the substitution group headed by this element. In a suitably enabled content model, a reference to the head·validates· not just the head itself, but elements corresponding to any member of the substitution group as well.
All such members must have type definitions which are either the same as the head‘s type definition or restrictions or extensions of it. Therefore, although the names of elements can vary widely as new namespaces and members of the substitution group are defined, the content of member elements is strictly limited according to the type definition of the substitution group head.
Note that element substitution groups are not represented as separate components. They are specified in the property values for element declarations (seeElement Declarations (§3.3)).
2.2.2.3 Attribute Declaration
An attribute declaration is an association between a name and a simple type definition, together with occurrence information and (optionally) a default value. The association is either global, or local to its containing complex type definition. Attribute declarations contribute to·validation· as part of complex type definition·validation·, when their occurrence, defaults and type components are checked against an attribute information item with a matching name and namespace.
For detailed information on attribute declarations, seeAttribute Declarations (§3.2).
2.2.2.4 Notation Declaration
A notation declaration is an association between a name and an identifier for a notation. For an attribute information item to be·valid· with respect to a NOTATION simple type definition, its value must have been declared with a notation declaration.
For detailed information on notation declarations, seeNotation Declarations (§3.12).
2.2.3 Model Group Components
The model group, particle, and wildcard components contribute to the portion of a complex type definition that controls an element information item‘s content.
2.2.3.1 Model Group
A model group is a constraint in the form of a grammar fragment that applies to lists of element information items. It consists of a list of particles, i.e. element declarations, wildcards and model groups. There are three varieties of model group:
Sequence (the element information items match the particles in sequential order); Conjunction (the element information items match the particles, in any order); Disjunction (the element information items match one of the particles).
For detailed information on model groups, seeModel Groups (§3.8).
2.2.3.2 Particle
A particle is a term in the grammar for element content, consisting of either an element declaration, a wildcard or a model group, together with occurrence constraints. Particles contribute to·validation· as part of complex type definition·validation·, when they allow anywhere from zero to many element information items or sequences thereof, depending on their contents and occurrence constraints.
A particle can be used in a complex type definition to constrain the·validation· of the[children] of an element information item; such a particle is called a content model.
NOTE: XML Schema: Structures·content models· are similar to but more expressive than[XML 1.0 (Second Edition)] content models; unlike[XML 1.0 (Second Edition)], XML Schema: Structures applies·content models· to the·validation· of both mixed and element-only content.
For detailed information on particles, seeParticles (§3.9).
2.2.3.3 Attribute Use
An attribute use plays a role similar to that of a particle, but for attribute declarations: an attribute declaration within a complex type definition is embedded within an attribute use, which specifies whether the declaration requires or merely allows its attribute, and whether it has a default or fixed value.
2.2.3.4 Wildcard
A wildcard is a special kind of particle which matches element and attribute information items dependent on their namespace name, independently of their local names.
For detailed information on wildcards, seeWildcards (§3.10).
2.2.4 Identity-constraint Definition Components
An identity-constraint definition is an association between a name and one of several varieties of identity-constraint related to uniqueness and reference. All the varieties use[XPath] expressions to pick out sets of information items relative to particular target element information items which are unique, or a key, or a·valid· reference, within a specified scope. An element information item is only·valid· with respect to an element declaration with identity-constraint definitions if those definitions are all satisfied for all the descendants of that element information item which they pick out.
For detailed information on identity-constraint definitions, seeIdentity-constraint Definitions (§3.11).
2.2.5 Group Definition Components
There are two kinds of convenience definitions provided to enable the re-use of pieces of complex type definitions: model group definitions and attribute group definitions.
2.2.5.1 Model Group Definition
A model group definition is an association between a name and a model group, enabling re-use of the same model group in several complex type definitions.
For detailed information on model group definitions, seeModel Group Definitions (§3.7).
2.2.5.2 Attribute Group Definition
An attribute group definition is an association between a name and a set of attribute declarations, enabling re-use of the same set in several complex type definitions.
For detailed information on attribute group definitions, seeAttribute Group Definitions (§3.6).
2.2.6 Annotation Components
An annotation is information for human and/or mechanical consumers. The interpretation of such information is not defined in this specification.
For detailed information on annotations, seeAnnotations (§3.13).
2.3 Constraints and Validation RulesThe[XML 1.0 (Second Edition)] specification describes two kinds of constraints on XML documents: well-formedness and validity constraints. Informally, the well-formedness constraints are those imposed by the definition of XML itself (such as the rules for the use of the < and > characters and the rules for proper nesting of elements), while validity constraints are the further constraints on document structure provided by a particular DTD.
The preceding section focused on·validation·, that is the constraints on information items which schema components supply. In fact however this specification provides four different kinds of normative statements about schema components, their representations in XML and their contribution to the·validation· of information items:
Schema Component ConstraintConstraints on the schema components themselves, i.e. conditions components must satisfy to be components at all. Located in the sixth sub-section of the per-component sections ofSchema Component Details (§3) and tabulated inSchema Component Constraints (§C.4).Schema Representation ConstraintConstraints on the representation of schema components in XML beyond those which are expressed inSchema for Schemas (normative) (§A). Located in the third sub-section of the per-component sections ofSchema Component Details (§3) and tabulated inSchema Representation Constraints (§C.3).Validation RulesContributions to·validation· associated with schema components. Located in the fourth sub-section of the per-component sections ofSchema Component Details (§3) and tabulated inValidation Rules (§C.1).Schema Information Set ContributionAugmentations to post-schema-validation infosets expressed by schema components, which follow as a consequence of·validation· and/or·assessment·. Located in the fifth sub-section of the per-component sections ofSchema Component Details (§3) and tabulated inContributions to the post-schema-validation infoset (§C.2).
The last of these, schema information set contributions, are not as new as they might at first seem. XML 1.0 validation augments the XML 1.0 information set in similar ways, for example by providing values for attributes not present in instances, and by implicitly exploiting type information for normalization or access. (As an example of the latter case, consider the effect of NMTOKENS on attribute white space, and the semantics of ID and IDREF.) By including schema information set contributions, this specification makes explicit some features that XML 1.0 left implicit.
2.4 ConformanceThis specification describes three levels of conformance for schema aware processors. The first is required of all processors. Support for the other two will depend on the application environments for which the processor is intended.
Minimally conforming processors must completely and correctly implement the·Schema Component Constraints·,·Validation Rules·, and·Schema Information Set Contributions· contained in this specification.
·Minimally conforming· processors which accept schemas represented in the form of XML documents as described inLayer 2: Schema Documents, Namespaces and Composition (§4.2) are additionally said to provide conformance to the XML Representation of Schemas. Such processors must, when processing schema documents, completely and correctly implement all·Schema Representation Constraints· in this specification, and must adhere exactly to the specifications inSchema Component Details (§3) for mapping the contents of such documents to·schema components· for use in·validation· and·assessment·.
NOTE: By separating the conformance requirements relating to the concrete syntax of XML schema documents, this specification admits processors which use schemas stored in optimized binary representations, dynamically created schemas represented as programming language data structures, or implementations in which particular schemas are compiled into executable code such as C or Java. Such processors can be said to be·minimally conforming· but not necessarily in·conformance to the XML Representation of Schemas·.
Fully conforming processors are network-enabled processors which are not only both·minimally conforming· and·in conformance to the XML Representation of Schemas·, but which additionally must be capable of accessing schema documents from the World Wide Web according toRepresentation of Schemas on the World Wide Web (§2.7) andHow schema definitions are located on the Web (§4.3.2). .
NOTE: Although this specification provides just these three standard levels of conformance, it is anticipated that other conventions can be established in the future. For example, the World Wide Web Consortium is considering conventions for packaging on the Web a variety of resources relating to individual documents and namespaces. Should such developments lead to new conventions for representing schemas, or for accessing them on the Web, new levels of conformance can be established and named at that time. There is no need to modify or republish this specification to define such additional levels of conformance.
SeeSchemas and Namespaces: Access and Composition (§4) for a more detailed explanation of the mechanisms supporting these levels of conformance.
2.5 Names and Symbol SpacesAs discussed inXML Schema Abstract Data Model (§2.2), most schema components (may) have·names·. If all such names were assigned from the same "pool", then it would be impossible to have, for example, a simple type definition and an element declaration both with the name "title" in a given·target namespace·.
Therefore this specification introduces the term symbol space to denote a collection of names, each of which is unique with respect to the others. A symbol space is similar to the non-normative concept ofnamespace partition introduced in[XML-Namespaces]. There is a single distinct symbol space within a given·target namespace· for each kind of definition and declaration component identified inXML Schema Abstract Data Model (§2.2), except that within a target namespace, simple type definitions and complex type definitions share a symbol space. Within a given symbol space, names are unique, but the same name may appear in more than one symbol space without conflict. For example, the same name can appear in both a type definition and an element declaration, without conflict or necessary relation between the two.
Locally scoped attribute and element declarations are special with regard to symbol spaces. Every complex type definition defines its own local attribute and element declaration symbol spaces, where these symbol spaces are distinct from each other and from any of the other symbol spaces. So, for example, two complex type definitions having the same target namespace can contain a local attribute declaration for the unqualified name "priority", or contain a local element declaration for the name "address", without conflict or necessary relation between the two.
2.6 Schema-Related Markup in Documents Being Validated2.6.1xsi:type
2.6.2xsi:nil
2.6.3xsi:schemaLocation, xsi:noNamespaceSchemaLocation
The XML representation of schema components uses a vocabulary identified by the namespace name http://www.w3.org/2001/XMLSchema. For brevity, the text and examples in this specification use the prefix xs: to stand for this namespace; in practice, any prefix can be used.
XML Schema: Structures also defines several attributes for direct use in any XML documents. These attributes are in a different namespace, which has the namespace name http://www.w3.org/2001/XMLSchema-instance. For brevity, the text and examples in this specification use the prefix xsi: to stand for this latter namespace; in practice, any prefix can be used. All schema processors have appropriate attribute declarations for these attributes built in, seeAttribute Declaration for the ‘type‘ attribute (§3.2.7),Attribute Declaration for the ‘nil‘ attribute (§3.2.7),Attribute Declaration for the ‘schemaLocation‘ attribute (§3.2.7) andAttribute Declaration for the ‘noNamespaceSchemaLocation‘ attribute (§3.2.7).
2.6.1 xsi:type
TheSimple Type Definition (§2.2.1.2) orComplex Type Definition (§2.2.1.3) used in·validation· of an element is usually determined by reference to the appropriate schema components. An element information item in an instance may, however, explicitly assert its type using the attribute xsi:type. The value of this attribute is a·QName·; seeQName Interpretation (§3.15.3) for the means by which the·QName· is associated with a type definition.
2.6.2 xsi:nil
XML Schema: Structures introduces a mechanism for signaling that an element should be accepted as·valid· when it has no content despite a content type which does not require or even necessarily allow empty content. An element may be·valid· without content if it has the attribute xsi:nil with the value true. An element so labeled must be empty, but can carry attributes if permitted by the corresponding complex type.
2.6.3 xsi:schemaLocation, xsi:noNamespaceSchemaLocation
The xsi:schemaLocation and xsi:noNamespaceSchemaLocation attributes can be used in a document to provide hints as to the physical location of schema documents which may be used for·assessment·. SeeHow schema definitions are located on the Web (§4.3.2) for details on the use of these attributes.
2.7 Representation of Schemas on the World Wide WebOn the World Wide Web, schemas are conventionally represented as XML documents (preferably of MIME type application/xml or text/xml, but see clause1.1 ofInclusion Constraints and Semantics (§4.2.1)), conforming to the specifications inLayer 2: Schema Documents, Namespaces and Composition (§4.2). For more information on the representation and use of schema documents on the World Wide Web seeStandards for representation of schemas and retrieval of schema documents on the Web (§4.3.1) andHow schema definitions are located on the Web (§4.3.2).
3 Schema Component Details
3.1 Introduction3.1.1Components and Properties
3.1.2XML Representations of Components
3.1.3The Mapping between XML Representations and Components
3.1.4White Space Normalization during Validation
The following sections provide full details on the composition of all schema components, together with their XML representations and their contributions to·assessment·. Each section is devoted to a single component, with separate subsections for
properties: their values and significance XML representation and the mapping to properties constraints on representation validation rules post-schema-validation infoset contributions constraints on the components themselves
The sub-sections immediately below introduce conventions and terminology used throughout the component sections.
3.1.1 Components and Properties
Components are defined in terms of their properties, and each property in turn is defined by giving its range, that is the values it may have. This can be understood as defining a schema as a labeled directed graph, where the root is a schema, every other vertex is a schema component or a literal (string, boolean, number) and every labeled edge is a property. The graph is not acyclic: multiple copies of components with the same name in the same·symbol space· may not exist, so in some cases re-entrant chains of properties must exist. Equality of components for the purposes of this specification is always defined as equality of names (including target namespaces) within symbol spaces.
NOTE: A schema and its components as defined in this chapter are an idealization of the information a schema-aware processor requires: implementations are not constrained in how they provide it. In particular, no implications about literal embedding versus indirection follow from the use below of language such as "properties . . . having . . . components as values".
Throughout this specification, the term absent is used as a distinguished property value denoting absence.
Any property not identified as optional is required to be present; optional properties which are not present are taken to have·absent· as their value. Any property identified as a having a set, subset or list value may have an empty value unless this is explicitly ruled out: this is not the same as·absent·. Any property value identified as a superset or subset of some set may be equal to that set, unless a proper superset or subset is explicitly called for. By ‘string‘ in Part 1 of this specification is meant a sequence of ISO 10646 characters identified aslegal XML characters in[XML 1.0 (Second Edition)].
3.1.2 XML Representations of Components
The principal purpose of XML Schema: Structures is to define a set of schema components that constrain the contents of instances and augment the information sets thereof. Although no external representation of schemas is required for this purpose, such representations will obviously be widely used. To provide for this in an appropriate and interoperable way, this specification provides a normative XML representation for schemas which makes provision for every kind of schema component. A document in this form (i.e. a
Two aspects of the XML representations of components presented in the following sections are constant across them all:
All of them allow attributes qualified with namespace names other than the XML Schema namespace itself: these appear as annotations in the corresponding schema component; All of them allow an
3.1.3 The Mapping between XML Representations and Components
For each kind of schema component there is a corresponding normative XML representation. The sections below describe the correspondences between the properties of each kind of schema component on the one hand and the properties of information items in that XML representation on the other, together with constraints on that representation above and beyond those implicit in theSchema for Schemas (normative) (§A).
The language used is as if the correspondences were mappings from XML representation to schema component, but the mapping in the other direction, and therefore the correspondence in the abstract, can always be constructed therefrom.
In discussing the mapping from XML representations to schema components below, the value of a component property is often determined by the value of an attribute information item, one of the[attributes] of an element information item. Since schema documents are constrained by theSchema for Schemas (normative) (§A), there is always a simple type definition associated with any such attribute information item. The phrase actual value is used to refer to the member of the value space of the simple type definition associated with an attribute information item which corresponds to its·normalized value·. This will often be a string, but may also be an integer, a boolean, a URI reference, etc. This term is also occasionally used with respect to element or attribute information items in a document being·validated·.
Many properties are identified below as having other schema components or sets of components as values. For the purposes of exposition, the definitions in this section assume that (unless the property is explicitly identified as optional) all such values are in fact present. When schema components are constructed from XML representations involving reference by name to other components, this assumption may be violated if one or more references cannot be resolved. This specification addresses the matter of missing components in a uniform manner, described inMissing Sub-components (§5.3): no mention of handling missing components will be found in the individual component descriptions below.
Forward reference to named definitions and declarations is allowed, both within and between·schema documents·. By the time the component corresponding to an XML representation which contains a forward reference is actually needed for·validation· an appropriately-named component may have become available to discharge the reference: seeSchemas and Namespaces: Access and Composition (§4) for details.
3.1.4 White Space Normalization during Validation
Throughout this specification, the initial value of some attribute information item is the value of the[normalized value] property of that item. Similarly, the initial value of an element information item is the string composed of, in order, the[character code] of each character information item in the[children] of that element information item.
The above definition means that comments and processing instructions, even in the midst of text, are ignored for all·validation· purposes.
The normalized value of an element or attribute information item is an·initial value· whose white space, if any, has been normalized according to the value of thewhiteSpace facet of the simple type definition used in its·validation·:
preserveNo normalization is done, the value is the·normalized value·replaceAll occurrences of #x9 (tab), #xA (line feed) and #xD (carriage return) are replaced with #x20 (space).collapseSubsequent to the replacements specified above under replace, contiguous sequences of #x20s are collapsed to a single #x20, and initial and/or final #x20s are deleted.
There are three alternative validation rules which may supply the necessary background for the above:Attribute Locally Valid (§3.2.4) (clause3),Element Locally Valid (Type) (§3.3.4) (clause3.1.3) orElement Locally Valid (Complex Type) (§3.4.4) (clause2.2).
These three levels of normalization correspond to the processing mandated in XML 1.0 for element content, CDATA attribute content and tokenized attributed content, respectively. SeeAttribute Value Normalization in[XML 1.0 (Second Edition)] for the precedent for replace and collapse for attributes. Extending this processing to element content is necessary to ensure a consistent·validation· semantics for simple types, regardless of whether they are applied to attributes or elements. Performing it twice in the case of attributes whose[normalized value] has already been subject to replacement or collapse on the basis of information in a DTD is necessary to ensure consistent treatment of attributes regardless of the extent to which DTD-based information has been made use of during infoset construction.
NOTE: Even when DTD-based information has been appealed to, andAttribute Value Normalization has taken place, the above definition of·normalized value· may mean further normalization takes place, as for instance when character entity references in attribute values result in white space characters other than spaces in their·initial value·s.
3.2 Attribute Declarations3.2.1The Attribute Declaration Schema Component
3.2.2XML Representation of Attribute Declaration Schema Components
3.2.3Constraints on XML Representations of Attribute Declarations
3.2.4Attribute Declaration Validation Rules
3.2.5Attribute Declaration Information Set Contributions
3.2.6Constraints on Attribute Declaration Schema Components
3.2.7Built-in Attribute Declarations
Attribute declarations provide for:
Local·validation· of attribute information item values using a simple type definition; Specifying default or fixed values for attribute information items.
Example
The XML representation of an attribute declaration.
3.2.1 The Attribute Declaration Schema Component
The attribute declaration schema component has the following properties:
Schema Component: Attribute Declaration
An NCName as defined by[XML-Namespaces].Either·absent· or a namespace name, as defined in[XML-Namespaces].A simple type definition.Optional. Either global or a complex type definition.Optional. A pair consisting of a value and one of default, fixed.Optional. An annotation.
The{name} property must match the local part of the names of attributes being·validated·.
The value of the attribute must conform to the supplied{type definition}.
A non-·absent· value of the{target namespace} property provides for·validation· of namespace-qualified attribute information items (which must be explicitly prefixed in the character-level form of XML documents).·Absent· values of{target namespace}·validate· unqualified (unprefixed) items.
A{scope} of global identifies attribute declarations available for use in complex type definitions throughout the schema. Locally scoped declarations are available for use only within the complex type definition identified by the{scope} property. This property is·absent· in the case of declarations within attribute group definitions: their scope will be determined when they are used in the construction of complex type definitions.
{value constraint} reproduces the functions of XML 1.0 default and #FIXED attribute values. default specifies that the attribute is to appear unconditionally in the post-schema-validation infoset, with the supplied value used whenever the attribute is not actually present; fixed indicates that the attribute value if present must equal the supplied constraint value, and if absent receives the supplied value as for default. Note that it is values that are supplied and/or checked, not strings.
SeeAnnotations (§3.13) for information on the role of the{annotation} property.
NOTE: A more complete and formal presentation of the semantics of{name},{target namespace} and{value constraint} is provided in conjunction with other aspects of complex type·validation· (seeElement Locally Valid (Complex Type) (§3.4.4).)
[XML-Infoset] distinguishes attributes with names such as xmlns or xmlns:xsl from ordinary attributes, identifying them as[namespace attributes]. Accordingly, it is unnecessary and in fact not possible for schemas to contain attribute declarations corresponding to such namespace declarations, seexmlns Not Allowed (§3.2.6). No means is provided in this specification to supply a default value for a namespace declaration.
3.2.2 XML Representation of Attribute Declaration Schema Components
The XML representation for an attribute declaration schema component is an
XML Representation Summary: attribute Element Information Item
default =string
fixed =string
form = (qualified | unqualified)
id =ID
name =NCName
ref =QName
type =QName
use = (optional | prohibited | required) : optional
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (simpleType?))
If the
Attribute Declaration Schema Component
Property Representation
{name} The·actual value· of the name[attribute]
{target namespace} The·actual value· of the targetNamespace[attribute] of the parent
{type definition} The simple type definition corresponding to the
{scope} global.
{value constraint} If there is a default or a fixed[attribute], then a pair consisting of the·actual value· (with respect to the{type definition}) of that[attribute] and either default or fixed, as appropriate, otherwise·absent·.
{annotation} The annotation corresponding to the
otherwise if the
Attribute Use Schema Component
Property Representation
{required} true if the use[attribute] is present with·actual value· required, otherwise false.
{attribute declaration} See the Attribute Declaration mapping immediately below.
{value constraint} If there is a default or a fixed[attribute], then a pair consisting of the·actual value· (with respect to the{type definition} of the{attribute declaration}) of that[attribute] and either default or fixed, as appropriate, otherwise·absent·.
Attribute Declaration Schema Component
Property Representation
{name} The·actual value· of the name[attribute]
{target namespace} If form is present and its·actual value· is qualified, or if form is absent and the·actual value· of attributeFormDefault on the
{type definition} The simple type definition corresponding to the
{scope} If the
{value constraint}·absent·.
{annotation} The annotation corresponding to the
otherwise (the
Attribute Use Schema Component
Property Representation
{required} true if the use[attribute] is present with·actual value· required, otherwise false.
{attribute declaration} The (top-level) attribute declaration·resolved· to by the·actual value· of the ref[attribute]
{value constraint} If there is a default or a fixed[attribute], then a pair consisting of the·actual value· (with respect to the{type definition} of the{attribute declaration}) of that[attribute] and either default or fixed, as appropriate, otherwise·absent·.
Attribute declarations can appear at the top level of a schema document, or within complex type definitions, either as complete (local) declarations, or by reference to top-level declarations, or within attribute group definitions. For complete declarations, top-level or local, the type attribute is used when the declaration can use a built-in or pre-declared simple type definition. Otherwise an anonymous
The default when no simple type definition is referenced or provided is the simple·ur-type definition·, which imposes no constraints at all.
Attribute information items·validated· by a top-level declaration must be qualified with the{target namespace} of that declaration (if this is·absent·, the item must be unqualified). Control over whether attribute information items·validated· by a local declaration must be similarly qualified or not is provided by the form[attribute], whose default is provided by the attributeFormDefault[attribute] on the enclosing
The names for top-level attribute declarations are in their own·symbol space·. The names of locally-scoped attribute declarations reside in symbol spaces local to the type definition which contains them.
3.2.3 Constraints on XML Representations of Attribute Declarations
Schema Representation Constraint: Attribute Declaration Representation OK
In addition to the conditions imposed on
2 If default and use are both present, use must have the·actual value· optional.
3 If the item‘s parent is not
3.2 If ref is present, then all of
4 type and
5 The corresponding attribute declaration must satisfy the conditions set out inConstraints on Attribute Declaration Schema Components (§3.2.6).
3.2.4 Attribute Declaration Validation Rules
Validation Rule: Attribute Locally Valid
For an attribute information item to be locally·valid· with respect to an attribute declaration all of the following must be true:1The declaration must not be·absent· (seeMissing Sub-components (§5.3) for how this can fail to be the case).
2Its{type definition} must not be absent.
3The item‘s·normalized value· must be locally·valid· with respect to that{type definition} as perString Valid (§3.14.4).
4 The item‘s·actual value· must match the value of the{value constraint}, if it is present and fixed.
Validation Rule: Schema-Validity Assessment (Attribute)
The schema-validity assessment of an attribute information item depends on its·validation· alone.
During·validation·, associations between element and attribute information items among the[children] and[attributes] on the one hand, and element and attribute declarations on the other, are established as a side-effect. Such declarations are called the context-determined declarations. See clause3.1 (inElement Locally Valid (Complex Type) (§3.4.4)) for attribute declarations, clause2 (inElement Sequence Locally Valid (Particle) (§3.9.4)) for element declarations.
For an attribute information item‘s schema-validity to have been assessed all of the following must be true:1 A non-·absent· attribute declaration must be known for it, namely one of the following:1.1 A declaration which has been established as its·context-determined declaration·;
1.2A declaration resolved to by its[local name] and[namespace name] as defined byQName resolution (Instance) (§3.15.4), provided its·context-determined declaration· is not skip.
2 Its·validity· with respect to that declaration must have been evaluated as perAttribute Locally Valid (§3.2.4).
3 Both clause1 and clause2 ofAttribute Locally Valid (§3.2.4) must be satisfied.
For attributes, there is no difference between assessment and strict assessment, so if the above holds, the attribute information item has been strictly assessed.
3.2.5 Attribute Declaration Information Set Contributions
Schema Information Set Contribution: Assessment Outcome (Attribute)
If the schema-validity of an attribute information item has been assessed as perSchema-Validity Assessment (Attribute) (§3.2.4), then in the post-schema-validation infoset it has properties as follows:PSVI Contributions for attribute information items
The nearest ancestor element information item with a[schema information] property.The appropriate case among the following:1 If it was·strictly assessed·, then the appropriate case among the following:1.1 If it was·valid· as defined byAttribute Locally Valid (§3.2.4), then valid;
1.2 otherwise invalid.
2 otherwise notKnown.
The appropriate case among the following:1 If it was·strictly assessed·, then full;
2 otherwise none.
infoset. SeeAttribute Default Value (§3.4.5) for the other possible value.
Schema Information Set Contribution: Validation Failure (Attribute)
If the local·validity·, as defined byAttribute Locally Valid (§3.2.4) above, of an attribute information item has been assessed, in the post-schema-validation infoset the item has a property:PSVI Contributions for attribute information items
The appropriate case among the following:1 If the item is not·valid·, then a list. Applications wishing to provide information as to the reason(s) for the·validation· failure are encouraged to record one or more error codes (seeOutcome Tabulations (normative) (§C)) herein.
2 otherwise·absent·.
Schema Information Set Contribution: Attribute Declaration
If an attribute information item is·valid· with respect to an attribute declaration as perAttribute Locally Valid (§3.2.4) then in the post-schema-validation infoset the attribute information item may, at processor option, have a property:PSVI Contributions for attribute information items
An·item isomorphic· to the declaration component itself.
Schema Information Set Contribution: Attribute Validated by Type
If clause3 ofAttribute Locally Valid (§3.2.4) applies with respect to an attribute information item, in the post-schema-validation infoset the attribute information item has a property:PSVI Contributions for attribute information items
The·normalized value· of the item as·validated·.
Furthermore, the item has one of the following alternative sets of properties:
EitherPSVI Contributions for attribute information items
An·item isomorphic· to the relevant attribute declaration‘s{type definition} component.If and only if that type definition has{variety} union, then an·item isomorphic· to that member of its{member type definitions} which actually·validated· the attribute item‘s[normalized value].
orPSVI Contributions for attribute information items
simple.The{target namespace} of the·type definition·.true if the{name} of the·type definition· is·absent·, otherwise false.The{name} of the·type definition·, if it is not·absent·. If it is·absent·, schema processors may, but need not, provide a value unique to the definition.
If the·type definition· has{variety} union, then calling that member of the{member type definitions} which actually·validated· the attribute item‘s·normalized value· the actual member type definition, there are three additional properties:PSVI Contributions for attribute information items
The{target namespace} of the·actual member type definition·.true if the{name} of the·actual member type definition· is·absent·, otherwise false.The{name} of the·actual member type definition·, if it is not·absent·. If it is·absent·, schema processors may, but need not, provide a value unique to the definition.
The first (·item isomorphic·) alternative above is provided for applications such as query processors which need access to the full range of details about an item‘s·assessment·, for example the type hierarchy; the second, for lighter-weight processors for whom representing the significant parts of the type hierarchy as information items might be a significant burden.
Also, if the declaration has a{value constraint}, the item has a property:PSVI Contributions for attribute information items
Thecanonical lexical representation of the declaration‘s{value constraint} value.
If the attribute information item was not·strictly assessed·, then instead of the values specified above,1 The item‘s[schema normalized value] property has the·initial value· of the item as its value;
2 The[type definition] and[member type definition] properties, or their alternatives, are based on the·simple ur-type definition·.
3.2.6 Constraints on Attribute Declaration Schema Components
All attribute declarations (seeAttribute Declarations (§3.2)) must satisfy the following constraints.
Schema Component Constraint: Attribute Declaration Properties Correct
All of the following must be true:1 The values of the properties of an attribute declaration must be as described in the property tableau inThe Attribute Declaration Schema Component (§3.2.1), modulo the impact ofMissing Sub-components (§5.3).
2 if there is a{value constraint}, thecanonical lexical representation of its value must be·valid· with respect to the{type definition} as defined inString Valid (§3.14.4).
3 If the{type definition} is or is derived fromID then there must not be a{value constraint}.
Schema Component Constraint: xmlns Not Allowed
The{name} of an attribute declaration must not match xmlns.NOTE: The{name} of an attribute is an·NCName·, which implicitly prohibits attribute declarations of the form xmlns:*.
Schema Component Constraint: xsi: Not Allowed
The{target namespace} of an attribute declaration, whether local or top-level, must not match http://www.w3.org/2001/XMLSchema-instance (unless it is one of the four built-in declarations given in the next section).NOTE: This reinforces the special status of these attributes, so that they not only need not be declared to be allowed in instances, but must not be declared. It also removes any temptation to experiment with supplying global or fixed values for e.g. xsi:type or xsi:nil, which would be seriously misleading, as they would have no effect.
3.2.7 Built-in Attribute Declarations
There are four attribute declarations present in every schema by definition:
Property Value
{name} type
{target namespace} http://www.w3.org/2001/XMLSchema-instance
{type definition} The built-inQName simple type definition
{scope} global
{value constraint}·absent·
{annotation}·absent·
Property Value
{name} nil
{target namespace} http://www.w3.org/2001/XMLSchema-instance
{type definition} The built-inboolean simple type definition
{scope} global
{value constraint}·absent·
{annotation}·absent·
Property Value
{name} schemaLocation
{target namespace} http://www.w3.org/2001/XMLSchema-instance
{type definition} An anonymous simple type definition, as follows: Property Value
{name}·absent·
{target namespace} http://www.w3.org/2001/XMLSchema-instance
{base type definition} The built in·simple ur-type definition·
{facets}·absent·
{variety} list
{item type definition} The built-inanyURI simple type definition
{annotation}·absent·
{scope} global
{value constraint}·absent·
{annotation}·absent·
Property Value
{name} noNamespaceSchemaLocation
{target namespace} http://www.w3.org/2001/XMLSchema-instance
{type definition} The built-inanyURI simple type definition
{scope} global
{value constraint}·absent·
{annotation}·absent·
3.3 Element Declarations3.3.1The Element Declaration Schema Component
3.3.2XML Representation of Element Declaration Schema Components
3.3.3Constraints on XML Representations of Element Declarations
3.3.4Element Declaration Validation Rules
3.3.5Element Declaration Information Set Contributions
3.3.6Constraints on Element Declaration Schema Components
Element declarations provide for:
Local·validation· of element information item values using a type definition; Specifying default or fixed values for an element information items; Establishing uniquenesses and reference constraint relationships among the values of related elements and attributes; Controlling the substitutability of elements through the mechanism of·element substitution groups·.
Example
XML representations of several different types of element declaration
3.3.1 The Element Declaration Schema Component
The element declaration schema component has the following properties:
Schema Component: Element Declaration
An NCName as defined by[XML-Namespaces].Either·absent· or a namespace name, as defined in[XML-Namespaces].Either a simple type definition or a complex type definition.Optional. Either global or a complex type definition.Optional. A pair consisting of a value and one of default, fixed.A boolean.A set of constraint definitions.Optional. A top-level element definition.A subset of {extension, restriction}.A subset of {substitution, extension, restriction}.A boolean.Optional. An annotation.
The{name} property must match the local part of the names of element information items being·validated·.
A{scope} of global identifies element declarations available for use in content models throughout the schema. Locally scoped declarations are available for use only within the complex type identified by the{scope} property. This property is·absent· in the case of declarations within named model groups: their scope is determined when they are used in the construction of complex type definitions.
A non-·absent· value of the{target namespace} property provides for·validation· of namespace-qualified element information items.·Absent· values of{target namespace}·validate· unqualified items.
An element information item is·valid· if it satisfies the{type definition}. For such an item, schema information set contributions appropriate to the{type definition} are added to the corresponding element information item in the post-schema-validation infoset.
If{nillable} is true, then an element may also be·valid· if it carries the namespace qualified attribute with[local name] nil from namespace http://www.w3.org/2001/XMLSchema-instance and value true (seexsi:nil (§2.6.2)) even if it has no text or element content despite a{content type} which would otherwise require content. Formal details of element·validation· are described inElement Locally Valid (Element) (§3.3.4).
{value constraint} establishes a default or fixed value for an element. If default is specified, and if the element being·validated· is empty, then the canonical form of the supplied constraint value becomes the[schema normalized value] of the·validated· element in the post-schema-validation infoset. If fixed is specified, then the element‘s content must either be empty, in which case fixed behaves as default, or its value must match the supplied constraint value.
NOTE: The provision of defaults for elements goes beyond what is possible in XML 1.0 DTDs, and does not exactly correspond to defaults for attributes. In particular, an element with a non-empty{value constraint} whose simple type definition includes the empty string in its lexical space will nonetheless never receive that value, because the{value constraint} will override it.
{identity-constraint definitions} express constraints establishing uniquenesses and reference relationships among the values of related elements and attributes. SeeIdentity-constraint Definitions (§3.11).
Element declarations are members of the substitution group, if any, identified by{substitution group affiliation}. Membership is transitive but not symmetric; an element declaration is a member of any group of which its{substitution group affiliation} is a member.
An empty{substitution group exclusions} allows a declaration to be nominated as the{substitution group affiliation} of other element declarations having the same{type definition} or types derived therefrom. The explicit values of{substitution group exclusions} rule out element declarations having types which are extensions or restrictions respectively of{type definition}. If both values are specified, then the declaration may not be nominated as the{substitution group affiliation} of any other declaration.
The supplied values for{disallowed substitutions} determine whether an element declaration appearing in a·content model· will be prevented from additionally·validating· elements (a) with anxsi:type (§2.6.1) that identifies an extension or restriction of the type of the declared element, and/or (b) from·validating· elements which are in the substitution group headed by the declared element. If{disallowed substitutions} is empty, then all derived types and substitution group members are allowed.
Element declarations for which{abstract} is true can appear in content models only when substitution is allowed; such declarations may not themselves ever be used to·validate· element content.
SeeAnnotations (§3.13) for information on the role of the{annotation} property.
3.3.2 XML Representation of Element Declaration Schema Components
The XML representation for an element declaration schema component is an
XML Representation Summary: element Element Information Item
abstract =boolean : false
block = (#all | List of (extension | restriction | substitution))
default =string
final = (#all | List of (extension | restriction))
fixed =string
form = (qualified | unqualified)
id =ID
maxOccurs = (nonNegativeInteger | unbounded) : 1
minOccurs =nonNegativeInteger : 1
name =NCName
nillable =boolean : false
ref =QName
substitutionGroup =QName
type =QName
{any attributes with non-schema namespace . . .}>
Content: (annotation?, ((simpleType |complexType)?, (unique |key |keyref)*))
If the
Element Declaration Schema Component
Property Representation
{name} The·actual value· of the name[attribute].
{target namespace} The·actual value· of the targetNamespace[attribute] of the parent
{scope} global.
{type definition} The type definition corresponding to the
{nillable} The·actual value· of the nillable[attribute], if present, otherwise false.
{value constraint} If there is a default or a fixed[attribute], then a pair consisting of the·actual value· (with respect to the{type definition}, if it is a simple type definition, or the{type definition}‘s{content type}, if that is a simple type definition, or else with respect to the built-instring simple type definition) of that[attribute] and either default or fixed, as appropriate, otherwise·absent·.
{identity-constraint definitions} A set consisting of the identity-constraint-definitions corresponding to all the
{substitution group affiliation} The element declaration·resolved· to by the·actual value· of the substitutionGroup[attribute], if present, otherwise·absent·.
{disallowed substitutions} A set depending on the·actual value· of the block[attribute], if present, otherwise on the·actual value· of the blockDefault[attribute] of the ancestor
2 If the EBV is #all, then {extension, restriction, substitution};
3 otherwise a set with members drawn from the set above, each being present or absent depending on whether the·actual value· (which is a list) contains an equivalently named item. NOTE: Although the blockDefault[attribute] of
{substitution group exclusions} As for{disallowed substitutions} above, but using the final and finalDefault[attributes] in place of the block and blockDefault[attributes] and with the relevant set being {extension, restriction}.
{abstract} The·actual value· of the abstract[attribute], if present, otherwise false.
{annotation} The annotation corresponding to the
otherwise if the
Particle Schema Component
Property Representation
{min occurs} The·actual value· of the minOccurs[attribute], if present, otherwise 1.
{max occurs} unbounded, if the maxOccurs[attribute] equals unbounded, otherwise the·actual value· of the maxOccurs[attribute], if present, otherwise 1.
{term} A (local) element declaration as given below.
An element declaration as in the first case above, with the exception of its{target namespace} and{scope} properties, which are as below:
Element Declaration Schema Component
Property Representation
{target namespace} If form is present and its·actual value· is qualified, or if form is absent and the·actual value· of elementFormDefault on the
{scope} If the
otherwise (the
Particle Schema Component
Property Representation
{min occurs} The·actual value· of the minOccurs[attribute], if present, otherwise 1.
{max occurs} unbounded, if the maxOccurs[attribute] equals unbounded, otherwise the·actual value· of the maxOccurs[attribute], if present, otherwise 1.
{term} The (top-level) element declaration·resolved· to by the·actual value· of the ref[attribute].
Element information items·validated· by a top-level declaration must be qualified with the{target namespace} of that declaration (if this is·absent·, the item must be unqualified). Control over whether element information items·validated· by a local declaration must be similarly qualified or not is provided by the form[attribute], whose default is provided by the elementFormDefault[attribute] on the enclosing
As noted above the names for top-level element declarations are in a separate·symbol space· from the symbol spaces for the names of type definitions, so there can (but need not be) a simple or complex type definition with the same name as a top-level element. As with attribute names, the names of locally-scoped element declarations with no{target namespace} reside in symbol spaces local to the type definition which contains them.
Note that the above allows for two levels of defaulting for unspecified type definitions. An
See below atXML Representation of Identity-constraint Definition Schema Components (§3.11.2) for
Example
The first example above declares an element whose type, by default, is the·ur-type definition·. The second uses an embedded anonymous complex type definition.
The last two examples illustrate the use of local element declarations. Instances of myLocalElement within contextOne will be constrained by myFirstType, while those within contextTwo will be constrained by mySecondType.
NOTE: The possibility that differing attribute declarations and/or content models would apply to elements with the same name in different contexts is an extension beyond the expressive power of a DTD in XML 1.0. Example
An example from a previous version of the schema for datatypes. The facet type is defined and the facet element is declared to use it. The facet element is abstract -- it‘s only defined to stand as the head for a substitution group. Two further elements are declared, each a member of the facet substitution group. Finally a type is defined which refers to facet, thereby allowing either period or encoding (or any other member of the group).
3.3.3 Constraints on XML Representations of Element Declarations
Schema Representation Constraint: Element Declaration Representation OK
In addition to the conditions imposed on
2 If the item‘s parent is not
2.2 If ref is present, then all of
3 type and either
4 The corresponding particle and/or element declarations must satisfy the conditions set out inConstraints on Element Declaration Schema Components (§3.3.6) andConstraints on Particle Schema Components (§3.9.6).
3.3.4 Element Declaration Validation Rules
Validation Rule: Element Locally Valid (Element)
For an element information item to be locally·valid· with respect to an element declaration all of the following must be true:1The declaration must not be·absent·.
2 Its{abstract} must be false.
3 The appropriate case among the following must be true:3.1 If{nillable} is false, then there must be no attribute information item among the element information item‘s[attributes] whose[namespace name] is identical to http://www.w3.org/2001/XMLSchema-instance and whose[local name] is nil.
3.2If{nillable} is true and there is such an attribute information item and its·actual value· is true , then all of the following must be true:3.2.1 The element information item must have no character or element information item[children].
3.2.2 There must be no fixed{value constraint}.
4 If there is an attribute information item among the element information item‘s[attributes] whose[namespace name] is identical to http://www.w3.org/2001/XMLSchema-instance and whose[local name] is type, then all of the following must be true:4.1 The·normalized value· of that attribute information item must be·valid· with respect to the built-inQName simple type, as defined byString Valid (§3.14.4);
4.2 The·local name· and·namespace name· (as defined inQName Interpretation (§3.15.3)), of the·actual value· of that attribute information item must resolve to a type definition, as defined inQName resolution (Instance) (§3.15.4) -- call this type definition the local type definition;
4.3 The·local type definition· must be validly derived from the{type definition} given the union of the{disallowed substitutions} and the{type definition}‘s{prohibited substitutions}, as defined inType Derivation OK (Complex) (§3.4.6) (if it is a complex type definition), or given{disallowed substitutions} as defined inType Derivation OK (Simple) (§3.14.6) (if it is a simple type definition).
The phrase actual type definition occurs below. If the above three clauses are satisfied, this should be understood as referring to the·local type definition·, otherwise to the{type definition}.
5 The appropriate case among the following must be true:5.1 If the declaration has a{value constraint}, the item has neither element nor character[children] and clause3.2 has not applied, then all of the following must be true:5.1.1 If the·actual type definition· is a·local type definition· then thecanonical lexical representation of the{value constraint} value must be a valid default for the·actual type definition· as defined inElement Default Valid (Immediate) (§3.3.6).
5.1.2 The element information item with thecanonical lexical representation of the{value constraint} value used as its·normalized value· must be·valid· with respect to the·actual type definition· as defined byElement Locally Valid (Type) (§3.3.4).
5.2 If the declaration has no{value constraint} or the item has either element or character[children] or clause3.2 has applied, then all of the following must be true:5.2.1 The element information item must be·valid· with respect to the·actual type definition· as defined byElement Locally Valid (Type) (§3.3.4).
5.2.2 If there is a fixed{value constraint} and clause3.2 has not applied, all of the following must be true:5.2.2.1 The element information item must have no element information item[children].
5.2.2.2 The appropriate case among the following must be true:5.2.2.2.1 If the{content type} of the·actual type definition· is mixed, then the·initial value· of the item must match thecanonical lexical representation of the{value constraint} value.
5.2.2.2.2 If the{content type} of the·actual type definition· is a simple type definition, then the·actual value· of the item must match thecanonical lexical representation of the{value constraint} value.
6 The element information item must be·valid· with respect to each of the{identity-constraint definitions} as perIdentity-constraint Satisfied (§3.11.4).
7 If the element information item is the·validation root·, it must be·valid· perValidation Root Valid (ID/IDREF) (§3.3.4).
Validation Rule: Element Locally Valid (Type)
For an element information item to be locally·valid· with respect to a type definition all of the following must be true:1The type definition must not be·absent·;
2 Its{abstract} must be false.
3 The appropriate case among the following must be true:3.1 If the type definition is a simple type definition, then all of the following must be true:3.1.1 The element information item‘s[attributes] must be empty, excepting those whose[namespace name] is identical to http://www.w3.org/2001/XMLSchema-instance and whose[local name] is one of type, nil, schemaLocation or noNamespaceSchemaLocation.
3.1.2 The element information item must have no element information item[children].
3.1.3If clause3.2 ofElement Locally Valid (Element) (§3.3.4) did not apply, then the·normalized value· must be·valid· with respect to the type definition as defined byString Valid (§3.14.4).
3.2 If the type definition is a complex type definition, then the element information item must be·valid· with respect to the type definition as perElement Locally Valid (Complex Type) (§3.4.4);
Validation Rule: Validation Root Valid (ID/IDREF)
For an element information item which is the·validation root· to be·valid· all of the following must be true:1 There must be no ID/IDREF binding in the item‘s[ID/IDREF table] whose[binding] is the empty set.
2There must be no ID/IDREF binding in the item‘s[ID/IDREF table] whose[binding] has more than one member.
SeeID/IDREF Table (§3.15.5) for the definition of ID/IDREF binding.NOTE: The first clause above applies when there is a reference to an undefined ID. The second applies when there is a multiply-defined ID. They are separated out to ensure that distinct error codes (seeOutcome Tabulations (normative) (§C)) are associated with these two cases. NOTE: Although this rule applies at the·validation root·, in practice processors, particularly streaming processors, may wish to detect and signal the clause2 case as it arises. NOTE: This reconstruction of[XML 1.0 (Second Edition)]‘s ID/IDREF functionality is imperfect in that if the·validation root· is not the document element of an XML document, the results will not necessarily be the same as those a validating parser would give were the document to have a DTD with equivalent declarations.
Validation Rule: Schema-Validity Assessment (Element)
The schema-validity assessment of an element information item depends on its·validation· and the·assessment· of its element information item children and associated attribute information items, if any.
So for an element information item‘s schema-validity to be assessed all of the following must be true:1One of the following must be true:1.1All of the following must be true:1.1.1 A non-·absent· element declaration must be known for it, because one of the following is true1.1.1.1 A declaration was stipulated by the processor (seeAssessing Schema-Validity (§5.2)).
1.1.1.2 A declaration has been established as its·context-determined declaration·.
1.1.1.3 All of the following must be true:1.1.1.3.1 Its·context-determined declaration· is not skip.
1.1.1.3.2 Its[local name] and[namespace name] resolve to an element declaration as defined byQName resolution (Instance) (§3.15.4).
1.1.2 Its·validity· with respect to that declaration must have been evaluated as perElement Locally Valid (Element) (§3.3.4).
1.1.3 If that evaluation involved the evaluation ofElement Locally Valid (Type) (§3.3.4), clause1 thereof must be satisfied.
1.2All of the following must be true:1.2.1 A non-·absent· type definition is known for it because one of the following is true1.2.1.1 A type definition was stipulated by the processor (seeAssessing Schema-Validity (§5.2)).
1.2.1.2 All of the following must be true:1.2.1.2.1 There is an attribute information item among the element information item‘s[attributes] whose[namespace name] is identical to http://www.w3.org/2001/XMLSchema-instance and whose[local name] is type.
1.2.1.2.2 The·normalized value· of that attribute information item is·valid· with respect to the built-inQName simple type, as defined byString Valid (§3.14.4).
1.2.1.2.3 The·local name· and·namespace name· (as defined inQName Interpretation (§3.15.3)), of the·actual value· of that attribute information item resolve to a type definition, as defined inQName resolution (Instance) (§3.15.4) -- call this type definition the local type definition.
1.2.1.2.4 If there is also a processor-stipulated type definition, the·local type definition· must be validly derived from that type definition given its{prohibited substitutions}, as defined inType Derivation OK (Complex) (§3.4.6) (if it is a complex type definition), or given the empty set, as defined inType Derivation OK (Simple) (§3.14.6) (if it is a simple type definition).
1.2.2 The element information item‘s·validity· with respect to the·local type definition· (if present and validly derived) or the processor-stipulated type definition (if no·local type definition· is present) has been evaluated as perElement Locally Valid (Type) (§3.3.4).
2 The schema-validity of all the element information items among its[children] has been assessed as perSchema-Validity Assessment (Element) (§3.3.4), and the schema-validity of all the attribute information items among its[attributes] has been assessed as perSchema-Validity Assessment (Attribute) (§3.2.4).
If either case of clause1 above holds, the element information item has been strictly assessed.
If the item cannot be·strictly assessed·, because neither clause1.1 nor clause1.2 above are satisfied, an element information item‘s schema validity may be laxly assessed if its·context-determined declaration· is not skip by·validating· with respect to the·ur-type definition· as perElement Locally Valid (Type) (§3.3.4).NOTE: In general if clause1.1 above holds clause1.2 does not, and vice versa. When an xsi:type[attribute] is involved, however, clause1.2 takes precedence, as is made clear inElement Locally Valid (Element) (§3.3.4).
NOTE: The{name} and{target namespace} properties are not mentioned above because they are checked during particle·validation·, as perElement Sequence Locally Valid (Particle) (§3.9.4).
3.3.5 Element Declaration Information Set Contributions
Schema Information Set Contribution: Assessment Outcome (Element)
If the schema-validity of an element information item has been assessed as perSchema-Validity Assessment (Element) (§3.3.4), then in the post-schema-validation infoset it has properties as follows:PSVI Contributions for element information items
The nearest ancestor element information item with a[schema information] property (or this element item itself if it has such a property).The appropriate case among the following:1 If it was·strictly assessed·, then the appropriate case among the following:1.1 If all of the following are true1.1.11.1.1.1 clause1.1 ofSchema-Validity Assessment (Element) (§3.3.4) applied and the item was·valid· as defined byElement Locally Valid (Element) (§3.3.4);
1.1.1.2 clause1.2 ofSchema-Validity Assessment (Element) (§3.3.4) applied and the item was·valid· as defined byElement Locally Valid (Type) (§3.3.4).
1.1.2 Neither its[children] nor its[attributes] contains an information item (element or attribute respectively) whose [validity] is invalid.
1.1.3 Neither its[children] nor its[attributes] contains an information item (element or attribute respectively) with a·context-determined declaration· of mustFind whose [validity] is unknown.
, then valid;
1.2 otherwise invalid..
2 otherwise notKnown.
The appropriate case among the following:1 If it was·strictly assessed· and neither its[children] nor its[attributes] contains an information item (element or attribute respectively) whose [validation attempted] is not full, then full;
2 If it was not·strictly assessed· and neither its[children] nor its[attributes] contains an information item (element or attribute respectively) whose [validation attempted] is not none, then none;
3 otherwise partial.
Schema Information Set Contribution: Validation Failure (Element)
If the local·validity·, as defined byElement Locally Valid (Element) (§3.3.4) above and/orElement Locally Valid (Type) (§3.3.4) below, of an element information item has been assessed, in the post-schema-validation infoset the item has a property:PSVI Contributions for element information items
The appropriate case among the following:1 If the item is not·valid·, then a list. Applications wishing to provide information as to the reason(s) for the·validation· failure are encouraged to record one or more error codes (seeOutcome Tabulations (normative) (§C)) herein.
2 otherwise·absent·.
Schema Information Set Contribution: Element Declaration
If an element information item is·valid· with respect to an element declaration as perElement Locally Valid (Element) (§3.3.4) then in the post-schema-validation infoset the element information item must, at processor option, have either:PSVI Contributions for element information items
an·item isomorphic· to the declaration component itself
orPSVI Contributions for element information items
true if clause3.2 ofElement Locally Valid (Element) (§3.3.4) above is satisfied, otherwise false
Schema Information Set Contribution: Element Validated by Type
If an element information item is·valid· with respect to a·type definition· as perElement Locally Valid (Type) (§3.3.4), in the post-schema-validation infoset the item has a property:PSVI Contributions for element information items
The appropriate case among the following:1 If clause3.2 ofElement Locally Valid (Element) (§3.3.4) andElement Default Value (§3.3.5) above have not applied and either the·type definition· is a simple type definition or its{content type} is a simple type definition, then the·normalized value· of the item as·validated·.
2 otherwise·absent·.
Furthermore, the item has one of the following alternative sets of properties:
EitherPSVI Contributions for element information items
An·item isomorphic· to the·type definition· component itself.If and only if that type definition is a simple type definition with{variety} union, or a complex type definition whose{content type} is a simple thype definition with{variety} union, then an·item isomorphic· to that member of the union‘s{member type definitions} which actually·validated· the element item‘s·normalized value·.
orPSVI Contributions for element information items
simple or complex, depending on the·type definition·.The {target namespace} of the·type definition·.true if the {name} of the·type definition· is·absent·, otherwise false.The {name} of the·type definition·, if it is not·absent·. If it is·absent·, schema processors may, but need not, provide a value unique to the definition.
If the·type definition· is a simple type definition or its{content type} is a simple type definition, and that type definition has{variety} union, then calling that member of the{member type definitions} which actually·validated· the element item‘s·normalized value· the actual member type definition, there are three additional properties:PSVI Contributions for element information items
The{target namespace} of the·actual member type definition·.true if the{name} of the·actual member type definition· is·absent·, otherwise false.The{name} of the·actual member type definition·, if it is not·absent·. If it is·absent·, schema processors may, but need not, provide a value unique to the definition.
The first (·item isomorphic·) alternative above is provided for applications such as query processors which need access to the full range of details about an item‘s·assessment·, for example the type hierarchy; the second, for lighter-weight processors for whom representing the significant parts of the type hierarchy as information items might be a significant burden.
Also, if the declaration has a{value constraint}, the item has a property:PSVI Contributions for element information items
Thecanonical lexical representation of the declaration‘s{value constraint} value.
Note that if an element is·laxly assessed·, then the[type definition] and[member type definition] properties, or their alternatives, are based on the·ur-type definition·.
Schema Information Set Contribution: Element Default Value
If the local·validity·, as defined byElement Locally Valid (Element) (§3.3.4) above, of an element information item has been assessed, in the post-schema-validation infoset the item has a property:PSVI Contributions for element information items
The appropriate case among the following:1 If the item is·valid· with respect to an element declaration as perElement Locally Valid (Element) (§3.3.4) and the{value constraint} is present, but clause3.2 ofElement Locally Valid (Element) (§3.3.4) above is not satisfied and the item has no element or character information item[children], then schema. Furthermore, the post-schema-validation infoset has thecanonical lexical representation of the{value constraint} value as the item‘s[schema normalized value] property.
2 otherwise infoset.
3.3.6 Constraints on Element Declaration Schema Components
All element declarations (seeElement Declarations (§3.3)) must satisfy the following constraint.
Schema Component Constraint: Element Declaration Properties Correct
All of the following must be true:1 The values of the properties of an element declaration must be as described in the property tableau inThe Element Declaration Schema Component (§3.3.1), modulo the impact ofMissing Sub-components (§5.3).
2 If there is a{value constraint}, thecanonical lexical representation of its value must be·valid· with respect to the{type definition} as defined inElement Default Valid (Immediate) (§3.3.6).
3 If there is an{substitution group affiliation}, the{type definition} of the element declaration must be validly derived from the{type definition} of the{substitution group affiliation}, given the value of the{substitution group exclusions} of the{substitution group affiliation}, as defined inType Derivation OK (Complex) (§3.4.6) (if the{type definition} is complex) or as defined inType Derivation OK (Simple) (§3.14.6) (if the{type definition} is simple).
4 If the{type definition} or{type definition}‘s{content type} is or is derived fromID then there must not be a{value constraint}.NOTE: The use ofID as a type definition for elements goes beyond XML 1.0, and should be avoided if backwards compatibility is desired.
The following constraints define relations appealed to elsewhere in this specification.
Schema Component Constraint: Element Default Valid (Immediate)
For a string to be a valid default with respect to a type definition the appropriate case among the following must be true:1 If the type definition is a simple type definition, then the string must be·valid· with respect to that definition as defined byString Valid (§3.14.4).
2 If the type definition is a complex type definition, then all of the following must be true:2.1 its{content type} must be a simple type definition or mixed.
2.2 The appropriate case among the following must be true:2.2.1 If the{content type} is a simple type definition, then the string must be·valid· with respect to that simple type definition as defined byString Valid (§3.14.4).
2.2.2 If the{content type} is mixed, then the{content type}‘s particle must be·emptiable· as defined byParticle Emptiable (§3.9.6).
Schema Component Constraint: Substitution Group OK (Transitive)
For an element declaration (call it D) together with a blocking constraint (a subset of {substitution, extension, restriction}, the value of a{disallowed substitutions}) to be validly substitutable for another element declaration (call it C) all of the following must be true:1 The blocking constraint does not contain substitution.
2 There is a chain of{substitution group affiliation}s from D to C, that is, either D‘s{substitution group affiliation} is C, or D‘s{substitution group affiliation}‘s{substitution group affiliation} is C, or . . .
3 The set of all{derivation method}s involved in the derivation of D‘s{type definition} from C‘s{type definition} does not intersect with the union of the blocking constraint, C‘s{prohibited substitutions} (if C is complex, otherwise the empty set) and the{prohibited substitutions} (respectively the empty set) of any intermediate{type definition}s in the derivation of D‘s{type definition} from C‘s{type definition}.
Schema Component Constraint: Substitution Group
Every element declaration in the{element declarations} of a schema defines a substitution group, a subset of those{element declarations}, as follows:1 The element declaration itself is in the group;
2 The group is closed with respect to{substitution group affiliation}, that is, if any element declaration in the{element declarations} has a{substitution group affiliation} in the group, then it is also in the group itself.
3.4 Complex Type Definitions3.4.1The Complex Type Definition Schema Component
3.4.2XML Representation of Complex Type Definitions
3.4.3Constraints on XML Representations of Complex Type Definitions
3.4.4Complex Type Definition Validation Rules
3.4.5Complex Type Definition Information Set Contributions
3.4.6Constraints on Complex Type Definition Schema Components
3.4.7Built-in Complex Type Definition
Complex Type Definitions provide for:
Constraining element information items by providingAttribute Declaration (§2.2.2.3)s governing the appearance and content of[attributes] Constraining element information item[children] to be empty, or to conform to a specified element-only or mixed content model, or else constraining the character information item[children] to conform to a specified simple type definition. Using the mechanisms ofType Definition Hierarchy (§2.2.1.1) to derive a complex type from another simple or complex type. Specifying·post-schema-validation infoset contributions· for elements. Limiting the ability to derive additional types from a given complex type. Controlling the permission to substitute, in an instance, elements of a derived type for elements declared in a content model to be of a given complex type.
Example
The XML representation of a complex type definition.
3.4.1 The Complex Type Definition Schema Component
A complex type definition schema component has the following properties:
Schema Component: Complex Type Definition
Optional. An NCName as defined by[XML-Namespaces].Either·absent· or a namespace name, as defined in[XML-Namespaces].Either a simple type definition or a complex type definition.Either extension or restriction.A subset of {extension, restriction}.A booleanA set of attribute uses.Optional. A wildcard.One of empty, a simple type definition or a pair consisting of a·content model· (I.e. aParticle (§2.2.3.2)) and one of mixed, element-only.A subset of {extension, restriction}.A set of annotations.
Complex types definitions are identified by their{name} and{target namespace}. Except for anonymous complex type definitions (those with no{name}), since type definitions (i.e. both simple and complex type definitions taken together) must be uniquely identified within an·XML Schema·, no complex type definition can have the same name as another simple or complex type definition. Complex type{name}s and{target namespace}s are provided for reference from instances (seexsi:type (§2.6.1)), and for use in the XML representation of schema components (specifically in
NOTE: The{name} of a complex type is not ipso facto the[(local) name] of the element information items·validated· by that definition. The connection between a name and a type definition is described inElement Declarations (§3.3).
As described inType Definition Hierarchy (§2.2.1.1), each complex type is derived from a{base type definition} which is itself either aSimple Type Definition (§2.2.1.2) or aComplex Type Definition (§2.2.1.3).{derivation method} specifies the means of derivation as either extension or restriction (seeType Definition Hierarchy (§2.2.1.1)).
A complex type with an empty specification for{final} can be used as a{base type definition} for other types derived by either of extension or restriction; the explicit values extension, and restriction prevent further derivations by extension and restriction respectively. If all values are specified, then the complex type is said to be final, because no further derivations are possible. Finality is not inherited, that is, a type definition derived by restriction from a type definition which is final for extension is not itself, in the absence of any explicit final attribute of its own, final for anything.
Complex types for which{abstract} is true must not be used as the{type definition} for the·validation· of element information items. It follows that they must not be referenced from anxsi:type (§2.6.1) attribute in an instance document. Abstract complex types can be used as{base type definition}s, or even as the{type definition}s of element declarations, provided in every case a concrete derived type definition is used for·validation·, either viaxsi:type (§2.6.1) or the operation of a substitution group.
{attribute uses} are a set of attribute uses. SeeElement Locally Valid (Complex Type) (§3.4.4) andAttribute Locally Valid (§3.2.4) for details of attribute·validation·.
{attribute wildcard}s provide a more flexible specification for·validation· of attributes not explicitly included in{attribute uses}. Informally, the specific values of{attribute wildcard} are interpreted as follows:
any:[attributes] can include attributes with any qualified or unqualified name. a set whose members are either namespace names or·absent·:[attributes] can include any attribute(s) from the specified namespace(s). If·absent· is included in the set, then any unqualified attributes are (also) allowed. ‘not‘ and a namespace name:[attributes] cannot include attributes from the specified namespace. ‘not‘ and·absent·:[attributes] cannot include unqualified attributes.
SeeElement Locally Valid (Complex Type) (§3.4.4) andWildcard allows Namespace Name (§3.10.4) for formal details of attribute wildcard·validation·.
{content type} determines the·validation· of[children] of element information items. Informally:
A{content type} with the distinguished value empty·validates· elements with no character or element information item[children]. A{content type} which is aSimple Type Definition (§2.2.1.2)·validates· elements with character-only[children]. An element-only{content type}·validates· elements with[children] that conform to the supplied·content model·. A mixed{content type}·validates· elements whose element[children] (i.e. specifically ignoring other[children] such as character information items) conform to the supplied·content model·.
{prohibited substitutions} determine whether an element declaration appearing in a· content model· is prevented from additionally·validating· element items with anxsi:type (§2.6.1) attribute that identifies a complex type definition derived by extension or restriction from this definition, or element items in a substitution group whose type definition is similarly derived: If{prohibited substitutions} is empty, then all such substitutions are allowed, otherwise, the derivation method(s) it names are disallowed.
SeeAnnotations (§3.13) for information on the role of the{annotations} property.
3.4.2 XML Representation of Complex Type Definitions
The XML representation for a complex type definition schema component is a
The XML representation for complex type definitions with a simple type definition{content type} is significantly different from that of those with other{content type}s, and this is reflected in the presentation below, which displays first the elements involved in the first case, then those for the second. The property mapping is shown once for each case.
XML Representation Summary: complexType Element Information Item
abstract =boolean : false
block = (#all | List of (extension | restriction))
final = (#all | List of (extension | restriction))
id =ID
mixed =boolean : false
name =NCName
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (simpleContent |complexContent | ((group |all |choice |sequence)?, ((attribute |attributeGroup)*,anyAttribute?))))
Whichever alternative for the content of
Complex Type Definition Schema Component
Property Representation
{name} The·actual value· of the name[attribute] if present, otherwise·absent·.
{target namespace} The·actual value· of the targetNamespace[attribute] of the
{abstract} The·actual value· of the abstract[attribute], if present, otherwise false.
{prohibited substitutions} A set corresponding to the·actual value· of the block[attribute], if present, otherwise on the·actual value· of the blockDefault[attribute] of the ancestor
2 If the EBV is #all, then {extension, restriction};
3 otherwise a set with members drawn from the set above, each being present or absent depending on whether the·actual value· (which is a list) contains an equivalently named item. NOTE: Although the blockDefault[attribute] of
{final} As for{prohibited substitutions} above, but using the final and finalDefault[attributes] in place of the block and blockDefault[attributes].
{annotations} The annotations corresponding to the
When the
id =ID
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (restriction |extension))
base =QName
id =ID
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (simpleType?, (minExclusive |minInclusive |maxExclusive |maxInclusive |totalDigits |fractionDigits |length |minLength |maxLength |enumeration |whiteSpace |pattern)*)?, ((attribute |attributeGroup)*,anyAttribute?))
base =QName
id =ID
{any attributes with non-schema namespace . . .}>
Content: (annotation?, ((attribute |attributeGroup)*,anyAttribute?))
id =ID
ref =QName
{any attributes with non-schema namespace . . .}>
Content: (annotation?)
id =ID
namespace = ((##any | ##other) | List of (anyURI | (##targetNamespace | ##local)) ) : ##any
processContents = (lax | skip | strict) : strict
{any attributes with non-schema namespace . . .}>
Content: (annotation?)
Complex Type Definition with simple content Schema Component
Property Representation
{base type definition} The type definition·resolved· to by the·actual value· of the base[attribute]
{derivation method} If the
{attribute uses} A union of sets of attribute uses as follows 1The set of attribute uses corresponding to the
2The{attribute uses} of the attribute groups·resolved· to by the·actual value·s of the ref[attribute] of the
3 if the type definition·resolved· to by the·actual value· of the base[attribute] is a complex type definition, the{attribute uses} of that type definition, unless the
3.2 what would have been the{name} and{target namespace} of the{attribute declaration} of an attribute use in the set per clause1 above but for the·actual value· of the use[attribute] of the relevant
{attribute wildcard} Let the local wildcard be defined as the appropriate case among the following: 1 If there is an
2 otherwise·absent·.
Let the complete wildcard be defined as the appropriate case among the following: 1 If there are no
2 If there are one or more
2.2If there is no
The value is then determined by the appropriate case among the following: 1 If the
2 If the
2.2 otherwise·absent·.
The value is then determined by the appropriate case among the following: 2.1 If the·base wildcard· is non-·absent·, then the appropriate case among the following: 2.1.1 If the·complete wildcard· is·absent·, then the·base wildcard·.
2.1.2otherwise a wildcard whose{process contents} and{annotation} are those of the·complete wildcard·, and whose{namespace constraint} is the intensional union of the{namespace constraint} of the·effective wildcard· and of the·base wildcard·, as defined inAttribute Wildcard Union (§3.10.6).
{content type} 1 if the type definition·resolved· to by the·actual value· of the base[attribute] is a complex type definition (whose own{content type} must be a simple type definition, see below) and the
1.2 otherwise (
a simple type definition which restricts that simple type definition with a set of facet components corresponding to the appropriate element information items among the
2 otherwise if the type definition·resolved· to by the·actual value· of the base[attribute] is a complex type definition (whose own{content type} must be a simple type definition, see below) and the
3 otherwise (the type definition·resolved· to by the·actual value· of the base[attribute] is a simple type definition and the
When the
The property mappings below are also used in the case where the third alternative (neither
id =ID
mixed =boolean
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (restriction |extension))
base =QName
id =ID
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (group |all |choice |sequence)?, ((attribute |attributeGroup)*,anyAttribute?))
base =QName
id =ID
{any attributes with non-schema namespace . . .}>
Content: (annotation?, ((group |all |choice |sequence)?, ((attribute |attributeGroup)*,anyAttribute?)))
Complex Type Definition with complex content Schema Component
Property Representation
{base type definition} The type definition·resolved· to by the·actual value· of the base[attribute]
{derivation method} If the
{attribute uses} A union of sets of attribute uses as follows: 1The set of attribute uses corresponding to the
2The{attribute uses} of the attribute groups·resolved· to by the·actual value·s of the ref[attribute] of the
3 The{attribute uses} of the type definition·resolved· to by the·actual value· of the base[attribute], unless the
3.2 what would have been the{name} and{target namespace} of the{attribute declaration} of an attribute use in the set per clause1 above but for the·actual value· of the use[attribute] of the relevant
{attribute wildcard} As above for the
{content type} The appropriate case among the following: 1 If the
1.1.2 There is an
1.1.3 There is a
, then empty;
1.2 otherwise a pair consisting of 1.2.1the appropriate case among the following: 1.2.1.1 If the mixed[attribute] is present on
1.2.1.2 If the mixed[attribute] is present on
1.2.1.3 otherwise elementOnly.
1.2.2 The particle corresponding to the
2 If the
2.2 If the type definition·resolved· to by the·actual value· of the base[attribute] has a{content type} of empty, then a pair of mixed or elementOnly (determined as per clause1.2.1 above) and the·explicit content· itself;
2.3 otherwise a pair of mixed or elementOnly (determined as per clause1.2.1 above) and a particle whose properties are as follows:{min occurs} 1{max occurs} 1{term} A model group whose{compositor} is sequence and whose{particles} are the particle of the{content type} of the type definition·resolved· to by the·actual value· of the base[attribute] followed by the·explicit content·.
NOTE: Aside from the simple coherence requirements enforced above, constraining type definitions identified as restrictions to actually be restrictions, that is, to·validate· a subset of the items which are·validated· by their base type definition, is enforced inConstraints on Complex Type Definition Schema Components (§3.4.6). NOTE: The only substantive function of the value prohibited for the use attribute of an
Careful consideration of the above concrete syntax reveals that a type definition need consist of no more than a name, i.e. that
Example
Three approaches to defining a type for length: one with character data content constrained by reference to a built-in datatype, and one attribute, the other two using two elements. length3 is the abbreviated alternative to length2: they correspond to identical type definition components.
Example
A type definition for personal names, and a definition derived by extension which adds a single element; an element declaration referencing the derived definition, and a·valid· instance thereof.
Example
A simplified type definition derived from the base type from the previous example by restriction, eliminating one optional daughter and fixing another to occur exactly once; an element declared by reference to it, and a·valid· instance thereof.
Example
A further illustration of the abbreviated form, with the mixed attribute appearing on complexType itself.
3.4.3 Constraints on XML Representations of Complex Type Definitions
Schema Representation Constraint: Complex Type Definition Representation OK
In addition to the conditions imposed on
2 If the
3 The corresponding complex type definition component must satisfy the conditions set out inConstraints on Complex Type Definition Schema Components (§3.4.6);
4 If clause2.1 or clause2.2 in the correspondence specification above for{attribute wildcard} is satisfied, the intensional intersection must be expressible, as defined inAttribute Wildcard Intersection (§3.10.6).
3.4.4 Complex Type Definition Validation Rules
Validation Rule: Element Locally Valid (Complex Type)
For an element information item to be locally·valid· with respect to a complex type definition all of the following must be true:1{abstract} is false.
2 If clause3.2 ofElement Locally Valid (Element) (§3.3.4) did not apply, then the appropriate case among the following must be true:2.1 If the{content type} is empty, then the element information item has no character or element information item[children].
2.2If the{content type} is a simple type definition, then the element information item has no element information item[children], and the·normalized value· of the element information item is·valid· with respect to that simple type definition as defined byString Valid (§3.14.4).
2.3 If the{content type} is element-only, then the element information item has no character information item[children] other than those whose[character code] is defined as awhite space in[XML 1.0 (Second Edition)].
2.4 If the{content type} is element-only or mixed, then the sequence of the element information item‘s element information item[children], if any, taken in order, is·valid· with respect to the{content type}‘s particle, as defined inElement Sequence Locally Valid (Particle) (§3.9.4).
3For each attribute information item in the element information item‘s[attributes] excepting those whose[namespace name] is identical to http://www.w3.org/2001/XMLSchema-instance and whose[local name] is one of type, nil, schemaLocation or noNamespaceSchemaLocation, the appropriate case among the following must be true:3.1If there is among the{attribute uses} an attribute use with an{attribute declaration} whose{name} matches the attribute information item‘s[local name] and whose{target namespace} is identical to the attribute information item‘s[namespace name] (where an·absent·{target namespace} is taken to be identical to a[namespace name] with no value), then the attribute information must be·valid· with respect to that attribute use as perAttribute Locally Valid (Use) (§3.5.4). In this case the{attribute declaration} of that attribute use is the·context-determined declaration· for the attribute information item with respect toSchema-Validity Assessment (Attribute) (§3.2.4) andAssessment Outcome (Attribute) (§3.2.5).
3.2otherwise all of the following must be true:3.2.1 There must be an{attribute wildcard}.
3.2.2 The attribute information item must be·valid· with respect to it as defined inItem Valid (Wildcard) (§3.10.4).
4 The{attribute declaration} of each attribute use in the{attribute uses} whose{required} is true matches one of the attribute information items in the element information item‘s[attributes] as per clause3.1 above.
5 Let the wild IDs be the set of all attribute information item to which clause3.2 applied and whose·validation· resulted in a·context-determined declaration· of mustFind or no·context-determined declaration· at all, and whose[local name] and[namespace name] resolve (as defined byQName resolution (Instance) (§3.15.4)) to an attribute declaration whose{type definition} is or is derived fromID. Then all of the following must be true:5.1 There must be no more than one item in·wild IDs·.
5.2 If·wild IDs· is non-empty, there must not be any attribute uses among the{attribute uses} whose{attribute declaration}‘s{type definition} is or is derived fromID.
NOTE: This clause serves to ensure that even via attribute wildcards no element has more than one attribute of type ID, and that even when an element legitimately lacks a declared attribute of type ID, a wildcard-validated attribute must not supply it. That is, if an element has a type whose attribute declarations include one of type ID, it either has that attribute or no attribute of type ID.
NOTE: When an{attribute wildcard} is present, this does not introduce any ambiguity with respect to how attribute information items for which an attribute use is present amongst the{attribute uses} whose name and target namespace match are·assessed·. In such cases the attribute use always takes precedence, and the·assessment· of such items stands or falls entirely on the basis of the attribute use and its{attribute declaration}. This follows from the details of clause3.
3.4.5 Complex Type Definition Information Set Contributions
Schema Information Set Contribution: Attribute Default Value
For each attribute use in the{attribute uses} whose{required} is false and whose{value constraint} is not·absent· but whose{attribute declaration} does not match one of the attribute information items in the element information item‘s[attributes] as per clause3.1 ofElement Locally Valid (Complex Type) (§3.4.4) above, the post-schema-validation infoset has an attribute information item whose properties are as below added to the[attributes] of the element information item.[local name]The{attribute declaration}‘s{name}.[namespace name]The{attribute declaration}‘s{target namespace}.[schema normalized value]Thecanonical lexical representation of the{value constraint} value.[schema default]Thecanonical lexical representation of the{value constraint} value.[validation context]The nearest ancestor element information item with a[schema information] property.[validity]valid.[validation attempted]full.[schema specified]schema.
The added items should also either have[type definition] (and[member type definition] if appropriate) properties, or their lighter-weight alternatives, as specified inAttribute Validated by Type (§3.2.5).
3.4.6 Constraints on Complex Type Definition Schema Components
All complex type definitions (seeComplex Type Definitions (§3.4)) must satisfy the following constraints.
Schema Component Constraint: Complex Type Definition Properties Correct
All of the following must be true:1 The values of the properties of a complex type definition must be as described in the property tableau inThe Complex Type Definition Schema Component (§3.4.1), modulo the impact ofMissing Sub-components (§5.3).
2 If the{base type definition} is a simple type definition, the{derivation method} must be extension.
3 Circular definitions are disallowed, except for the·ur-type definition·. That is, it must be possible to reach the·ur-type definition· by repeatedly following the{base type definition}.
4 Two distinct attribute declarations in the{attribute uses} must not have identical{name}s and{target namespace}s.
5 Two distinct attribute declarations in the{attribute uses} must not have{type definition}s which are or are derived fromID.
Schema Component Constraint: Derivation Valid (Extension)
If the{derivation method} is extension, the appropriate case among the following must be true:1 If the{base type definition} is a complex type definition, then all of the following must be true:1.1 The{final} of the{base type definition} must not contain extension.
1.2Its{attribute uses} must be a subset of the{attribute uses} of the complex type definition itself, that is, for every attribute use in the{attribute uses} of the{base type definition}, there must be an attribute use in the{attribute uses} of the complex type definition itself whose{attribute declaration} has the same{name},{target namespace} and{type definition} as its attribute declaration.
1.3 If it has an{attribute wildcard}, the complex type definition must also have one, and the base type definition‘s{attribute wildcard}‘s{namespace constraint} must be a subset of the complex type definition‘s{attribute wildcard}‘s{namespace constraint}, as defined byWildcard Subset (§3.10.6).
1.4 One of the following must be true:1.4.1 The{content type} of the{base type definition} and the{content type} of the complex type definition itself must be the same simple type definition.
1.4.2 All of the following must be true:1.4.2.1 The{content type} of the complex type definition itself must specify a particle.
1.4.2.2 One of the following must be true:1.4.2.2.1 The{content type} of the{base type definition} must be empty.
1.4.2.2.2 All of the following must be true:1.4.2.2.2.1 Both{content type}s must be mixed or both must be element-only.
1.4.2.2.2.2 The particle of the complex type definition must be a·valid extension· of the{base type definition}‘s particle, as defined inParticle Valid (Extension) (§3.9.6).
1.5 It must in principle be possible to derive the complex type definition in two steps, the first an extension and the second a restriction (possibly vacuous), from that type definition among its ancestors whose{base type definition} is the·ur-type definition·.NOTE: This requirement ensures that nothing removed by a restriction is subsequently added back by an extension. It is trivial to check if the extension in question is the only extension in its derivation, or if there are no restrictions bar the first from the·ur-type definition·.
Constructing the intermediate type definition to check this constraint is straightforward: simply re-order the derivation to put all the extension steps first, then collapse them into a single extension. If the resulting definition can be the basis for a valid restriction to the desired definition, the constraint is satisfied.
2 If the{base type definition} is a simple type definition, then all of the following must be true:2.1 The{content type} must be the same simple type definition.
2.2 The{final} of the{base type definition} must not contain extension.
If this constraintDerivation Valid (Extension) (§3.4.6) holds of a complex type definition, it is a valid extension of its{base type definition}.
Schema Component Constraint: Derivation Valid (Restriction, Complex)
If the{derivation method} is restriction all of the following must be true:1 The{base type definition} must be a complex type definition whose{final} does not contain restriction.
2For each attribute use (call this R) in the{attribute uses} the appropriate case among the following must be true:2.1 If there is an attribute use in the{attribute uses} of the{base type definition} (call this B) whose{attribute declaration} has the same{name} and{target namespace}, then all of the following must be true:2.1.1 one of the following must be true:2.1.1.1 B‘s{required} is false.
2.1.1.2 R‘s{required} is true.
2.1.2 R‘s{attribute declaration}‘s{type definition} must be validly derived from B‘s{type definition} given the empty set as defined inType Derivation OK (Simple) (§3.14.6).
2.1.3 Let the effective value constraint of an attribute use be its{value constraint}, if present, otherwise its{attribute declaration}‘s{value constraint} . Then one of the following must be true:2.1.3.1 B‘s·effective value constraint· is·absent· or default.
2.1.3.2 R‘s·effective value constraint· is fixed with the same string as B‘s.
2.2 otherwise the{base type definition} must have an{attribute wildcard} and the{target namespace} of the R‘s{attribute declaration} must be·valid· with respect to that wildcard, as defined inWildcard allows Namespace Name (§3.10.4).
3For each attribute use in the{attribute uses} of the{base type definition} whose{required} is true, there must be an attribute use with an{attribute declaration} with the same{name} and{target namespace} as its{attribute declaration} in the{attribute uses} of the complex type definition itself whose{required} is true.
4If there is an{attribute wildcard}, all of the following must be true:4.1 The{base type definition} must also have one.
4.2 The complex type definition‘s{attribute wildcard}‘s{namespace constraint} must be a subset of the{base type definition}‘s{attribute wildcard}‘s{namespace constraint}, as defined byWildcard Subset (§3.10.6).
5 The appropriate case among the following must be true:5.1 If the{content type} of the complex type definition is a simple type definition, then one of the following must be true:5.1.1 The{content type} of the{base type definition} must be a simple type definition of which the{content type} is a·valid restriction· as defined inDerivation Valid (Restriction, Simple) (§3.14.6).
5.1.2 The{base type definition} must be mixed and have a particle which is·emptiable· as defined inParticle Emptiable (§3.9.6).
5.2 If the{content type} of the complex type itself is empty , then one of the following must be true:5.2.1 The{content type} of the{base type definition} must also be empty.
5.2.2 The{content type} of the{base type definition} must be elementOnly or mixed and have a particle which is·emptiable· as defined inParticle Emptiable (§3.9.6).
5.3 If the{content type} of the{base type definition} is mixed or the{content type} of the complex type definition itself is element-only, then the particle of the complex type definition itself must be a·valid restriction· of the particle of the{content type} of the{base type definition} as defined inParticle Valid (Restriction) (§3.9.6).
If this constraintDerivation Valid (Restriction, Complex) (§3.4.6) holds of a complex type definition, it is a valid restriction of its{base type definition}.
NOTE: To restrict a complex type definition with a simple base type definition to empty, use a simple type definition with a fixed value of the empty string: this preserves the type information.
The following constraint defines a relation appealed to elsewhere in this specification.
Schema Component Constraint: Type Derivation OK (Complex)
For a complex type definition (call it D, for derived) to be validly derived from a type definition (call this B, for base) given a subset of {extension, restriction} all of the following must be true:1 If B and D are not the same type definition, then the{derivation method} of D must not be in the subset.
2 One of the following must be true:2.1 B and D must be the same type definition.
2.2 B must be D‘s{base type definition}.
2.3 All of the following must be true:2.3.1 D‘s{base type definition} must not be the·ur-type definition·.
2.3.2 The appropriate case among the following must be true:2.3.2.1 If D‘s{base type definition} is complex, then it must be validly derived from B given the subset as defined by this constraint.
2.3.2.2 If D‘s{base type definition} is simple, then it must be validly derived from B given the subset as defined inType Derivation OK (Simple) (§3.14.6).
NOTE: This constraint is used to check that when someone uses a type in a context where another type was expected (either via xsi:type or substitution groups), that the type used is actually derived from the expected type, and that that derivation does not involve a form of derivation which was ruled out by the expected type.
3.4.7 Built-in Complex Type Definition
There is a complex type definition nearly equivalent to the·ur-type definition· present in every schema by definition. It has the following properties:
Property Value
{name} anyType
{target namespace} http://www.w3.org/2001/XMLSchema
{base type definition} Itself
{derivation method} restriction
{content type} A pair consisting of mixed and a particle with the following properties: Property Value
{min occurs} 1
{max occurs} 1
{term} a model group with the following properties: Property Value
{compositor} sequence
{particles} a list containing one particle with the following properties: Property Value
{min occurs} 0
{max occurs} unbounded
{term} a wildcard with an any{namespace constraint}
{attribute uses} The empty set
{attribute wildcard}{namespace constraint} is any
{final} The empty set
{prohibited substitutions} The empty set
{abstract} false
The mixed content specification together with the unconstrained wildcard content model and attribute specification produce the defining property for the·ur-type definition·, namely that every complex type definition is (eventually) a restriction of the·ur-type definition·: its permissions and requirements are the least restrictive possible.
NOTE: This specification does not provide an inventory of built-in complex type definitions for use in user schemas. A preliminary library of complex type definitions is available which includes both mathematical (e.g. rational) and utility (e.g. array) type definitions. In particular, there is a text type definition which is recommended for use as the type definition in element declarations intended for general text content, as it makes sensible provision for various aspects of internationalization. For more details, see the schema document for the type library at its namespace name:http://www.w3.org/2001/03/XMLSchema/TypeLibrary.xsd.
3.5 AttributeUses3.5.1The Attribute Use Schema Component
3.5.2XML Representation of Attribute Use Components
3.5.3Constraints on XML Representations of Attribute Uses
3.5.4Attribute Use Validation Rules
3.5.5Attribute Use Information Set Contributions
3.5.6Constraints on Attribute Use Schema Components
An attribute use is a utility component which controls the occurrence and defaulting behavior of attribute declarations. It plays the same role for attribute declarations in complex types that particles play for element declarations.
Example
XML representations which all involve attribute uses, illustrating some of the possibilities for controlling occurrence.
3.5.1 The Attribute Use Schema Component
The attribute use schema component has the following properties:
Schema Component: Attribute Use
A boolean.An attribute declaration.Optional. A pair consisting of a value and one of default, fixed.
{required} determines whether this use of an attribute declaration requires an appropriate attribute information item to be present, or merely allows it.
{attribute declaration} provides the attribute declaration itself, which will in turn determine the simple type definition used.
{value constraint} allows for local specification of a default or fixed value. This must be consistent with that of the{attribute declaration}, in that if the{attribute declaration} specifies a fixed value, the only allowed{value constraint} is the same fixed value.
3.5.2 XML Representation of Attribute Use Components
Attribute uses correspond to all uses of
3.5.3 Constraints on XML Representations of Attribute Uses
None as such.
3.5.4 Attribute Use Validation Rules
Validation Rule: Attribute Locally Valid (Use)
For an attribute information item to be·valid· with respect to an attribute use its·normalized value· must match thecanonical lexical representation of the attribute use‘s{value constraint} value, if it is present and fixed.
3.5.5 Attribute Use Information Set Contributions
None as such.
3.5.6 Constraints on Attribute Use Schema Components
All attribute uses (seeAttributeUses (§3.5)) must satisfy the following constraints.
Schema Component Constraint: Attribute Use Correct
All of the following must be true:1 The values of the properties of an attribute use must be as described in the property tableau inThe Attribute Use Schema Component (§3.5.1), modulo the impact ofMissing Sub-components (§5.3).
2 If the{attribute declaration} has a fixed{value constraint}, then if the attribute use itself has a{value constraint}, it must also be fixed and its value must match that of the{attribute declaration}‘s{value constraint}.
3.6 Attribute Group Definitions3.6.1The Attribute Group Definition Schema Component
3.6.2XML Representation of Attribute Group Definition Schema Components
3.6.3Constraints on XML Representations of Attribute Group Definitions
3.6.4Attribute Group Definition Validation Rules
3.6.5Attribute Group Definition Information Set Contributions
3.6.6Constraints on Attribute Group Definition Schema Components
A schema can name a group of attribute declarations so that they may be incorporated as a group into complex type definitions.
Attribute group definitions do not participate in·validation· as such, but the{attribute uses} and{attribute wildcard} of one or more complex type definitions may be constructed in whole or part by reference to an attribute group. Thus, attribute group definitions provide a replacement for some uses of XML‘sparameter entity facility. Attribute group definitions are provided primarily for reference from the XML representation of schema components (see
Example
XML representations for attribute group definitions. The effect is as if the attribute declarations in the group were present in the type definition.
3.6.1 The Attribute Group Definition Schema Component
The attribute group definition schema component has the following properties:
Schema Component: Attribute Group Definition
An NCName as defined by[XML-Namespaces].Either·absent· or a namespace name, as defined in[XML-Namespaces].A set of attribute uses.Optional. A wildcard.Optional. An annotation.
Attribute groups are identified by their{name} and{target namespace}; attribute group identities must be unique within an·XML Schema·. SeeReferences to schema components across namespaces (§4.2.3) for the use of component identifiers when importing one schema into another.
{attribute uses} is a set attribute uses, allowing for local specification of occurrence and default or fixed values.
{attribute wildcard} provides for an attribute wildcard to be included in an attribute group. See above underComplex Type Definitions (§3.4) for the interpretation of attribute wildcards during·validation·.
SeeAnnotations (§3.13) for information on the role of the{annotation} property.
3.6.2 XML Representation of Attribute Group Definition Schema Components
The XML representation for an attribute group definition schema component is an
XML Representation Summary: attributeGroup Element Information Item
id =ID
name =NCName
ref =QName
{any attributes with non-schema namespace . . .}>
Content: (annotation?, ((attribute |attributeGroup)*,anyAttribute?))
When an
Attribute Group Definition Schema Component
Property Representation
{name} The·actual value· of the name[attribute]
{target namespace} The·actual value· of the targetNamespace[attribute] of the parent schema element information item.
{attribute uses} The union of the set of attribute uses corresponding to the
{attribute wildcard} As for the·complete wildcard· as described inXML Representation of Complex Type Definitions (§3.4.2).
{annotation} The annotation corresponding to the
The example above illustrates a pattern which recurs in the XML representation of schemas: The same element, in this case attributeGroup, serves both to define and to incorporate by reference. In the first case the name attribute is required, in the second the ref attribute is required, and the element must be empty. These two are mutually exclusive, and also conditioned by context: the defining form, with a name, must occur at the top level of a schema, whereas the referring form, with a ref, must occur within a complex type definition or an attribute group definition.
3.6.3 Constraints on XML Representations of Attribute Group Definitions
Schema Representation Constraint: Attribute Group Definition Representation OK
In addition to the conditions imposed on
2 If clause2.1 or clause2.2 in the correspondence specification inXML Representation of Complex Type Definitions (§3.4.2) for{attribute wildcard}, as referenced above, is satisfied, the intensional intersection must be expressible, as defined inAttribute Wildcard Intersection (§3.10.6).
3 Circular group reference is disallowed outside
3.6.4 Attribute Group Definition Validation Rules
None as such.
3.6.5 Attribute Group Definition Information Set Contributions
None as such.
3.6.6 Constraints on Attribute Group Definition Schema Components
All attribute group definitions (seeAttribute Group Definitions (§3.6)) must satisfy the following constraint.
Schema Component Constraint: Attribute Group Definition Properties Correct
All of the following must be true:1 The values of the properties of an attribute group definition must be as described in the property tableau inThe Attribute Group Definition Schema Component (§3.6.1), modulo the impact ofMissing Sub-components (§5.3);
2 Two distinct members of the{attribute uses} must not have{attribute declaration}s both of whose{name}s match and whose{target namespace}s are identical.
3 Two distinct members of the{attribute uses} must not have{attribute declaration}s both of whose{type definition}s are or are derived fromID.
3.7 Model Group Definitions3.7.1The Model Group Definition Schema Component
3.7.2XML Representation of Model Group Definition Schema Components
3.7.3Constraints on XML Representations of Model Group Definitions
3.7.4Model Group Definition Validation Rules
3.7.5Model Group Definition Information Set Contributions
3.7.6Constraints on Model Group Definition Schema Components
A model group definition associates a name and optional annotations with aModel Group (§2.2.3.1). By reference to the name, the entire model group can be incorporated by reference into a{term}.
Model group definitions are provided primarily for reference from theXML Representation of Complex Type Definitions (§3.4.2) (see
Example
A minimal model group is defined and used by reference, first as the whole content model, then as one alternative in a choice.
3.7.1 The Model Group Definition Schema Component
The model group definition schema component has the following properties:
Schema Component: Model Group Definition
An NCName as defined by[XML-Namespaces].Either·absent· or a namespace name, as defined in[XML-Namespaces].A model group.Optional. An annotation.
Model group definitions are identified by their{name} and{target namespace}; model group identities must be unique within an·XML Schema·. SeeReferences to schema components across namespaces (§4.2.3) for the use of component identifiers when importing one schema into another.
Model group definitions per se do not participate in·validation·, but the{term} of a particle may correspond in whole or in part to a model group from a model group definition.
{model group} is theModel Group (§2.2.3.1) for which the model group definition provides a name.
SeeAnnotations (§3.13) for information on the role of the{annotation} property.
3.7.2 XML Representation of Model Group Definition Schema Components
The XML representation for a model group definition schema component is a
XML Representation Summary: group Element Information Item
name =NCName>
Content: (annotation?, (all |choice |sequence))
If there is a name[attribute] (in which case the item will have
Model Group Definition Schema Component
Property Representation
{name} The·actual value· of the name[attribute]
{target namespace} The·actual value· of the targetNamespace[attribute] of the parent schema element information item.
{model group} A model group which is the{term} of a particle corresponding to the
{annotation} The annotation corresponding to the
Otherwise, the item will have a ref[attribute], in which case it corresponds to a particle component with properties as follows (unless minOccurs=maxOccurs=0, in which case the item corresponds to no component at all):
Particle Schema Component
Property Representation
{min occurs} The·actual value· of the minOccurs[attribute], if present, otherwise 1.
{max occurs} unbounded, if the maxOccurs[attribute] equals unbounded, otherwise the·actual value· of the maxOccurs[attribute], if present, otherwise 1.
{term} The{model group} of the model group definition·resolved· to by the·actual value· of the ref[attribute]
The name of this section is slightly misleading, in that the second, un-named, case above (with a ref and no name) is not really a named model group at all, but a reference to one. Also note that in the first (named) case above no reference is made to minOccurs or maxOccurs: this is because the schema for schemas does not allow them on the child of
Given the constraints on its appearance in content models, an
3.7.3 Constraints on XML Representations of Model Group Definitions
Schema Representation Constraint: Model Group Definition Representation OK
In addition to the conditions imposed on
3.7.4 Model Group Definition Validation Rules
None as such.
3.7.5 Model Group Definition Information Set Contributions
None as such.
3.7.6 Constraints on Model Group Definition Schema Components
All model group definitions (seeModel Group Definitions (§3.7)) must satisfy the following constraint.
Schema Component Constraint: Model Group Definition Properties Correct
The values of the properties of a model group definition must be as described in the property tableau inThe Model Group Definition Schema Component (§3.7.1), modulo the impact ofMissing Sub-components (§5.3).
3.8 Model Groups3.8.1The Model Group Schema Component
3.8.2XML Representation of Model Group Schema Components
3.8.3Constraints on XML Representations of Model Groups
3.8.4Model Group Validation Rules
3.8.5Model Group Information Set Contributions
3.8.6Constraints on Model Group Schema Components
When the[children] of element information items are not constrained to be empty or by reference to a simple type definition (Simple Type Definitions (§3.14)), the sequence of element information item[children] content may be specified in more detail with a model group. Because the{term} property of a particle can be a model group, and model groups contain particles, model groups can indirectly contain other model groups; the grammar for content models is therefore recursive.
Example
XML representations for the three kinds of model group, the third nested inside the second.
3.8.1 The Model Group Schema Component
The model group schema component has the following properties:
Schema Component: Model Group
One of all, choice or sequence.A list of particlesOptional. An annotation.
specifies a sequential (sequence), disjunctive (choice) or conjunctive (all) interpretation of the{particles}. This in turn determines whether the element information item[children]·validated· by the model group must:
(sequence) correspond, in order, to the specified{particles}; (choice) corresponded to exactly one of the specified{particles}; (all) contain all and only exactly zero or one of each element specified in{particles}. The elements can occur in any order. In this case, to reduce implementation complexity,{particles} is restricted to contain local and top-level element declarations only, with{min occurs}=0 or 1,{max occurs}=1.
When two or more particles contained directly or indirectly in the{particles} of a model group have identically named element declarations as their{term}, the type definitions of those declarations must be the same. By ‘indirectly‘ is meant particles within the{particles} of a group which is itself the{term} of a directly contained particle, and so on recursively.
SeeAnnotations (§3.13) for information on the role of the{annotation} property.
3.8.2 XML Representation of Model Group Schema Components
The XML representation for a model group schema component is either an
XML Representation Summary: all Element Information Item
id =ID
maxOccurs = 1 : 1
minOccurs = (0 | 1) : 1
{any attributes with non-schema namespace . . .}>
Content: (annotation?,element*)
id =ID
maxOccurs = (nonNegativeInteger | unbounded) : 1
minOccurs =nonNegativeInteger : 1
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (element |group |choice |sequence |any)*)
id =ID
maxOccurs = (nonNegativeInteger | unbounded) : 1
minOccurs =nonNegativeInteger : 1
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (element |group |choice |sequence |any)*)
Each of the above items corresponds to a particle containing a model group, with properties as follows (unless minOccurs=maxOccurs=0, in which case the item corresponds to no component at all):
Particle Schema Component
Property Representation
{min occurs} The·actual value· of the minOccurs[attribute], if present, otherwise 1.
{max occurs} unbounded, if the maxOccurs[attribute] equals unbounded, otherwise the·actual value· of the maxOccurs[attribute], if present, otherwise 1.
{term} A model group as given below:
Model Group Schema Component
Property Representation
{compositor} One of all, choice, sequence depending on the element information item.
{particles} A sequence of particles corresponding to all the
{annotation} The annotation corresponding to the
3.8.3 Constraints on XML Representations of Model Groups
Schema Representation Constraint: Model Group Representation OK
In addition to the conditions imposed on
3.8.4 Model Group Validation Rules
Validation Rule: Element Sequence Valid
Define a partition of a sequence as a sequence of sub-sequences, some or all of which may be empty, such that concatenating all the sub-sequences yields the original sequence.
For a sequence (possibly empty) of element information items to be locally·valid· with respect to a model group the appropriate case among the following must be true:1 If the{compositor} is sequence, then there must be a·partition· of the sequence into n sub-sequences where n is the length of{particles} such that each of the sub-sequences in order is·valid· with respect to the corresponding particle in the{particles} as defined inElement Sequence Locally Valid (Particle) (§3.9.4).
2 If the{compositor} is choice, then there must be a particle among the{particles} such that the sequence is·valid· with respect to that particle as defined inElement Sequence Locally Valid (Particle) (§3.9.4).
3 If the{compositor} is all, then there must be a·partition· of the sequence into n sub-sequences where n is the length of{particles} such that there is a one-to-one mapping between the sub-sequences and the{particles} where each sub-sequence is·valid· with respect to the corresponding particle as defined inElement Sequence Locally Valid (Particle) (§3.9.4).
Nothing in the above should be understood as ruling out groups whose{particles} is empty: although no sequence can be·valid· with respect to such a group whose{compositor} is choice, the empty sequence is·valid· with respect to empty groups whose{compositor} is sequence or all.
NOTE: The above definition is implicitly non-deterministic, and should not be taken as a recipé for implementations. Note in particular that when{compositor} is all, particles is restricted to a list of local and top-level element declarations (seeConstraints on Model Group Schema Components (§3.8.6)). A much simpler implementation is possible than would arise from a literal interpretation of the definition above; informally, the content is·valid· when each declared element occurs exactly once (or at most once, if{min occurs} is 0), and each is·valid· with respect to its corresponding declaration. The elements can occur in arbitrary order.
3.8.5 Model Group Information Set Contributions
None as such.
3.8.6 Constraints on Model Group Schema Components
All model groups (seeModel Groups (§3.8)) must satisfy the following constraints.
Schema Component Constraint: Model Group Correct
All of the following must be true:1 The values of the properties of a model group must be as described in the property tableau inThe Model Group Schema Component (§3.8.1), modulo the impact ofMissing Sub-components (§5.3).
2 Circular groups are disallowed. That is, within the{particles} of a group there must not be at any depth a particle whose{term} is the group itself.
Schema Component Constraint: All Group Limited
When a model group has{compositor} all all of the following must be true:1 one of the following must be true:1.1 It appears as the model group of a model group definition.
1.2 It appears in a particle with{min occurs}={max occurs}=1, and that particle must be part of a pair which constitutes the{content type} of a complex type definition.
2 The{max occurs} of all the particles in the{particles} of the group must be 0 or 1.
Schema Component Constraint: Element Declarations Consistent
If the{particles} contains, either directly, indirectly (that is, within the{particles} of a contained model group, recursively) or·implicitly· two or more element declaration particles with the same{name} and{target namespace}, then all their type definitions must be the same top-level definition, that is, all of the following must be true:1 all their{type definition}s must have a non-·absent· name.
2 all their{type definition}s must have the same name.
3 all their{type definition}s must have the same target namespace.
A list of particles implicitly contains an element declaration if a member of the list contains that element declaration in its·substitution group·.
Schema Component Constraint: Unique Particle Attribution
A content model must be formed such that during·validation· of an element information item sequence, the particle contained directly, indirectly or·implicitly· therein with which to attempt to·validate· each item in the sequence in turn can be uniquely determined without examining the content or attributes of that item, and without any information about the items in the remainder of the sequence.NOTE: This constraint reconstructs for XML Schema the equivalent constraints of[XML 1.0 (Second Edition)] and SGML. Given the presence of element substitution groups and wildcards, the concise expression of this constraint is difficult, seeAnalysis of the Unique Particle Attribution Constraint (non-normative) (§H) for further discussion.
NOTE: Because locally-scoped element declarations may or may not have a{target namespace}, the scope of declarations is not relevant to enforcing either of the two preceding constraints.
The following constraints define relations appealed to elsewhere in this specification.
Schema Component Constraint: Effective Total Range (all and sequence)
The effective total range of a particle whose{term} is a group whose{compositor} is all or sequence is a pair of minimum and maximum, as follows:minimumThe product of the particle‘s{min occurs} and the sum of the{min occurs} of every wildcard or element declaration particle in the group‘s{particles} and the minimum part of the effective total range of each of the group particles in the group‘s{particles} (or 0 if there are no{particles}).maximumunbounded if the{max occurs} of any wildcard or element declaration particle in the group‘s{particles} or the maximum part of the effective total range of any of the group particles in the group‘s{particles} is unbounded, or if any of those is non-zero and the{max occurs} of the particle itself is unbounded, otherwise the product of the particle‘s{max occurs} and the sum of the{max occurs} of every wildcard or element declaration particle in the group‘s{particles} and the maximum part of the effective total range of each of the group particles in the group‘s{particles} (or 0 if there are no{particles}).
Schema Component Constraint: Effective Total Range (choice)
The effective total range of a particle whose{term} is a group whose{compositor} is choice is a pair of minimum and maximum, as follows:minimumThe product of the particle‘s{min occurs} and the minimum of the{min occurs} of every wildcard or element declaration particle in the group‘s{particles} and the minimum part of the effective total range of each of the group particles in the group‘s{particles} (or 0 if there are no{particles}).maximumunbounded if the{max occurs} of any wildcard or element declaration particle in the group‘s{particles} or the maximum part of the effective total range of any of the group particles in the group‘s{particles} is unbounded, or if any of those is non-zero and the{max occurs} of the particle itself is unbounded, otherwise the product of the particle‘s{max occurs} and the maximum of the{max occurs} of every wildcard or element declaration particle in the group‘s{particles} and the maximum part of the effective total range of each of the group particles in the group‘s{particles} (or 0 if there are no{particles}).
3.9 Particles3.9.1The Particle Schema Component
3.9.2XML Representation of Particle Components
3.9.3Constraints on XML Representations of Particles
3.9.4Particle Validation Rules
3.9.5Particle Information Set Contributions
3.9.6Constraints on Particle Schema Components
As described inModel Groups (§3.8), particles contribute to the definition of content models.
Example
XML representations which all involve particles, illustrating some of the possibilities for controlling occurrence.
3.9.1 The Particle Schema Component
The particle schema component has the following properties:
Schema Component: Particle
A non-negative integer.Either a non-negative integer or unbounded.One of a model group, a wildcard, or an element declaration.
In general, multiple element information item[children], possibly with intervening character[children] if the content type is mixed, can be·validated· with respect to a single particle. When the{term} is an element declaration or wildcard,{min occurs} determines the minimum number of such element[children] that can occur. The number of such children must be greater than or equal to{min occurs}. If{min occurs} is 0, then occurrence of such children is optional.
Again, when the{term} is an element declaration or wildcard, the number of such element[children] must be less than or equal to any numeric specification of{max occurs}; if{max occurs} is unbounded, then there is no upper bound on the number of such children.
When the{term} is a model group, the permitted occurrence range is determined by a combination of{min occurs} and{max occurs} and the occurrence ranges of the{term}‘s{particles}.
3.9.2 XML Representation of Particle Components
Particles correspond to all three elements (
3.9.3 Constraints on XML Representations of Particles
None as such.
3.9.4 Particle Validation Rules
Validation Rule: Element Sequence Locally Valid (Particle)
For a sequence (possibly empty) of element information items to be locally·valid· with respect to a particle the appropriate case among the following must be true:1If the{term} is a wildcard, then all of the following must be true:1.1 The length of the sequence must be greater than or equal to the{min occurs}.
1.2 If{max occurs} is a number, the length of the sequence must be less than or equal to the{max occurs}.
1.3 Each element information item in the sequence must be·valid· with respect to the wildcard as defined byItem Valid (Wildcard) (§3.10.4).
2If the{term} is an element declaration, then all of the following must be true:2.1 The length of the sequence must be greater than or equal to the{min occurs}.
2.2 If{max occurs} is a number, the length of the sequence must be less than or equal to the{max occurs}.
2.3 For each element information item in the sequence one of the following must be true:2.3.1 The element declaration is local (i.e. its{scope} must not be global), its{abstract} is false, the element information item‘s[namespace name] is identical to the element declaration‘s{target namespace} (where an·absent·{target namespace} is taken to be identical to a[namespace name] with no value) and the element information item‘s[local name] matches the element declaration‘s{name}.
In this case the element declaration is the·context-determined declaration· for the element information item with respect toSchema-Validity Assessment (Element) (§3.3.4) andAssessment Outcome (Element) (§3.3.5).
2.3.2 The element declaration is top-level (i.e. its{scope} is global),{abstract} is false, the element information item‘s[namespace name] is identical to the element declaration‘s{target namespace} (where an·absent·{target namespace} is taken to be identical to a[namespace name] with no value) and the element information item‘s[local name] matches the element declaration‘s{name}.
In this case the element declaration is the·context-determined declaration· for the element information item with respect toSchema-Validity Assessment (Element) (§3.3.4) andAssessment Outcome (Element) (§3.3.5).
2.3.3The element declaration is top-level (i.e. its{scope} is global), its{disallowed substitutions} does not contain substitution, the[local ] and[namespace name] of the element information item resolve to an element declaration, as defined inQName resolution (Instance) (§3.15.4) -- call this declaration the substituting declaration and the·substituting declaration· together with the particle‘s element declaration‘s{disallowed substitutions} is validly substitutable for the particle‘s element declaration as defined inSubstitution Group OK (Transitive) (§3.3.6).
In this case the·substituting declaration· is the·context-determined declaration· for the element information item with respect toSchema-Validity Assessment (Element) (§3.3.4) andAssessment Outcome (Element) (§3.3.5).
3 If the{term} is a model group, then all of the following must be true:3.1 There is a·partition· of the sequence into n sub-sequences such that n is greater than or equal to{min occurs}.
3.2 If{max occurs} is a number, n must be less than or equal to{max occurs}.
3.3 Each sub-sequence in the·partition· is·valid· with respect to that model group as defined inElement Sequence Valid (§3.8.4).
NOTE: Clauses clause1 and clause2.3.3 do not interact: an element information item validatable by a declaration with a substitution group head in a different namespace is not validatable by a wildcard which accepts the head‘s namespace but not its own.
3.9.5 Particle Information Set Contributions
None as such.
3.9.6 Constraints on Particle Schema Components
All particles (seeParticles (§3.9)) must satisfy the following constraints.
Schema Component Constraint: Particle Correct
All of the following must be true:1 The values of the properties of a particle must be as described in the property tableau inThe Particle Schema Component (§3.9.1), modulo the impact ofMissing Sub-components (§5.3).
2 If{max occurs} is not unbounded, that is, it has a numeric value, then all of the following must be true:2.1{min occurs} must not be greater than{max occurs}.
2.2{max occurs} must be greater than or equal to 1.
The following constraints define relations appealed to elsewhere in this specification.
Schema Component Constraint: Particle Valid (Extension)
For a particle (call it E, for extension) to be a valid extension of another particle (call it B, for base) one of the following must be true:1 They are the same particle.
2 E‘s{min occurs}={max occurs}=1 and its{term} is a sequence group whose{particles}‘ first member is a particle all of whose properties, recursively, are identical to those of B, with the exception of {annotation} properties.
The approach to defining a type by restricting another type definition set out here is designed to ensure that types defined in this way are guaranteed to be a subset of the type they restrict. This is accomplished by requiring a clear mapping between the components of the base type definition and the restricting type definition. Permissible mappings are set out below via a set of recursive definitions, bottoming out in the obvious cases, e.g. where an (restricted) element declaration corresponds to another (base) element declaration with the same name and type but the same or wider range of occurrence.
NOTE: The structural correspondence approach to guaranteeing the subset relation set out here is necessarily verbose, but has the advantage of being checkable in a straightforward way. The working group solicits feedback on how difficult this is in practice, and on whether other approaches are found to be viable. Schema Component Constraint: Particle Valid (Restriction)
For a particle (call it R, for restriction) to be a valid restriction of another particle (call it B, for base) one of the following must be true:1 They are the same particle.
2 depending on the kind of particle, per the table below, with the qualifications that all of the following must be true:2.1 Any top-level element declaration particle (in R or B) which is the{substitution group affiliation} of one or more other element declarations is treated as if it were a choice group whose{min occurs} and{max occurs} are those of the particle, and whose{particles} consists of one particle with{min occurs} and{max occurs} of 1 for the top-level element declaration and for each of the declarations in its·substitution group·.
2.2 Any pointless occurrences of
2.2.2 All of the following must be true:2.2.2.1 The particle within which this
2.2.2.2 One of the following must be true:2.2.2.2.1 The
2.2.2.2.2 The particle within which this
2.2.2{particles} has only one member.
2.2.2 All of the following must be true:2.2.2.1 The particle within which this
2.2.2.2 One of the following must be true:2.2.2.2.1 The
2.2.2.2.2 The particle within which this
Base Particle
elt any all choice sequence
Derived Particle eltNameAnd- TypeOKNSCompatRecurse- AsIfGroupRecurse- AsIfGroupRecurseAs- IfGroup
any ForbiddenNSSubset Forbidden Forbidden Forbidden
all ForbiddenNSRecurse- CheckCardinalityRecurse Forbidden Forbidden
choice ForbiddenNSRecurse- CheckCardinality ForbiddenRecurseLax Forbidden
seq- uence ForbiddenNSRecurse- CheckCardinalityRecurse- UnorderedMapAndSumRecurse
Schema Component Constraint: Occurrence Range OK
For a particle‘s occurrence range to be a valid restriction of another‘s occurrence range all of the following must be true:1 Its{min occurs} is greater than or equal to the other‘s{min occurs}.
2 one of the following must be true:2.1 The other‘s{max occurs} is unbounded.
2.2 Both{max occurs} are numbers, and the particle‘s is less than or equal to the other‘s.
Schema Component Constraint: Particle Restriction OK (Elt:Elt -- NameAndTypeOK)
For an element declaration particle to be a·valid restriction· of another element declaration particle all of the following must be true:1 The declarations‘{name}s and{target namespace}s are the same.
2 Either B‘s{nillable} is true or R‘s{nillable} is false.
3 R‘s occurrence range is a valid restriction of B‘s occurrence range as defined byOccurrence Range OK (§3.9.6).
4 either B‘s declaration‘s{value constraint} is absent, or is not fixed, or R‘s declaration‘s{value constraint} is fixed with the same value.
5 R‘s declaration‘s{identity-constraint definitions} is a subset of B‘s declaration‘s{identity-constraint definitions}, if any.
6 R‘s declaration‘s{disallowed substitutions} is a superset of B‘s declaration‘s{disallowed substitutions}.
7 R‘s{type definition} is validly derived given {extension, list, union} from B‘s{type definition} as defined byType Derivation OK (Complex) (§3.4.6) orType Derivation OK (Simple) (§3.14.6), as appropriate.
NOTE: The above constraint on{type definition} means that in deriving a type by restriction, any contained type definitions must themselves be explicitly derived by restriction from the corresponding type definitions in the base definition.
Schema Component Constraint: Particle Derivation OK (Elt:Any -- NSCompat)
For an element declaration particle to be a·valid restriction· of a wildcard particle all of the following must be true:1 The element declaration‘s{target namespace} is·valid· with respect to the wildcard‘s{namespace constraint} as defined byWildcard allows Namespace Name (§3.10.4).
2 R‘s occurrence range is a valid restriction of B‘s occurrence range as defined byOccurrence Range OK (§3.9.6).
Schema Component Constraint: Particle Derivation OK (Elt:All/Choice/Sequence -- RecurseAsIfGroup)
For an element declaration particle to be a·valid restriction· of a group particle (all, choice or sequence) a group particle of the variety corresponding to B‘s, with{min occurs} and{max occurs} of 1 and with{particles} consisting of a single particle the same as the element declaration must be a·valid restriction· of the group as defined byParticle Derivation OK (All:All,Sequence:Sequence -- Recurse) (§3.9.6),Particle Derivation OK (Choice:Choice -- RecurseLax) (§3.9.6) orParticle Derivation OK (All:All,Sequence:Sequence -- Recurse) (§3.9.6), depending on whether the group is all, choice or sequence.
Schema Component Constraint: Particle Derivation OK (Any:Any -- NSSubset)
For a wildcard particle to be a·valid restriction· of another wildcard particle all of the following must be true:1 R‘s occurrence range must be a valid restriction of B‘s occurrence range as defined byOccurrence Range OK (§3.9.6).
2 R‘s{namespace constraint} must be an intensional subset of B‘s{namespace constraint} as defined byWildcard Subset (§3.10.6).
Schema Component Constraint: Particle Derivation OK (All/Choice/Sequence:Any -- NSRecurseCheckCardinality)
For a group particle to be a·valid restriction· of a wildcard particle all of the following must be true:1 Every member of the{particles} of the group is a·valid restriction· of the wildcard as defined byParticle Valid (Restriction) (§3.9.6).
2 The effective total range of the group, as defined byEffective Total Range (all and sequence) (§3.8.6) (if the group is all or sequence) orEffective Total Range (choice) (§3.8.6) (if it is choice) is a valid restriction of B‘s occurrence range as defined byOccurrence Range OK (§3.9.6).
Schema Component Constraint: Particle Derivation OK (All:All,Sequence:Sequence -- Recurse)
For an all or sequence group particle to be a·valid restriction· of another group particle with the same{compositor} all of the following must be true:1 R‘s occurrence range is a valid restriction of B‘s occurrence range as defined byOccurrence Range OK (§3.9.6).
2 There is a complete·order-preserving· functional mapping from the particles in the{particles} of R to the particles in the{particles} of B such that all of the following must be true:2.1 Each particle in the{particles} of R is a·valid restriction· of the particle in the{particles} of B it maps to as defined byParticle Valid (Restriction) (§3.9.6).
2.2 All particles in the{particles} of B which are not mapped to by any particle in the{particles} of R are·emptiable· as defined byParticle Emptiable (§3.9.6).
NOTE: Although the·validation· semantics of an all group does not depend on the order of its particles, derived all groups are required to match the order of their base in order to simplify checking that the derivation is OK. A complete functional mapping is order-preserving if each particle r in the domain R maps to a particle b in the range B which follows (not necessarily immediately) the particle in the range B mapped to by the predecessor of r, if any, where "predecessor" and "follows" are defined with respect to the order of the lists which constitute R and B.
Schema Component Constraint: Particle Derivation OK (Choice:Choice -- RecurseLax)
For a choice group particle to be a·valid restriction· of another choice group particle all of the following must be true:1 R‘s occurrence range is a valid restriction of B‘s occurrence range as defined byOccurrence Range OK (§3.9.6);
2 There is a complete·order-preserving· functional mapping from the particles in the{particles} of R to the particles in the{particles} of B such that each particle in the{particles} of R is a·valid restriction· of the particle in the{particles} of B it maps to as defined byParticle Valid (Restriction) (§3.9.6).
NOTE: Although the·validation· semantics of a choice group does not depend on the order of its particles, derived choice groups are required to match the order of their base in order to simplify checking that the derivation is OK.
Schema Component Constraint: Particle Derivation OK (Sequence:All -- RecurseUnordered)
For a sequence group particle to be a·valid restriction· of an all group particle all of the following must be true:1 R‘s occurrence range is a valid restriction of B‘s occurrence range as defined byOccurrence Range OK (§3.9.6).
2 There is a complete functional mapping from the particles in the{particles} of R to the particles in the{particles} of B such that all of the following must be true:2.1 No particle in the{particles} of B is mapped to by more than one of the particles in the{particles} of R;
2.2 Each particle in the{particles} of R is a·valid restriction· of the particle in the{particles} of B it maps to as defined byParticle Valid (Restriction) (§3.9.6);
2.3 All particles in the{particles} of B which are not mapped to by any particle in the{particles} of R are·emptiable· as defined byParticle Emptiable (§3.9.6).
NOTE: Although this clause allows reordering, because of the limits on the contents of all groups the checking process can still be deterministic.
Schema Component Constraint: Particle Derivation OK (Sequence:Choice -- MapAndSum)
For a sequence group particle to be a·valid restriction· of a choice group particle all of the following must be true:1 There is a complete functional mapping from the particles in the{particles} of R to the particles in the{particles} of B such that each particle in the{particles} of R is a·valid restriction· of the particle in the{particles} of B it maps to as defined byParticle Valid (Restriction) (§3.9.6).
2 The pair consisting of the product of the{min occurs} of R and the length of its{particles} and unbounded if{max occurs} is unbounded otherwise the product of the{max occurs} of R and the length of its{particles} is a valid restriction of B‘s occurrence range as defined byOccurrence Range OK (§3.9.6).NOTE: This clause is in principle more restrictive than absolutely necessary, but in practice will cover all the likely cases, and is much easier to specify than the fully general version.
NOTE: This case allows the "unfolding" of iterated disjunctions into sequences. It may be particularly useful when the disjunction is an implicit one arising from the use of substitution groups.
Schema Component Constraint: Particle Emptiable
For a particle to be emptiable one of the following must be true:1 Its{min occurs} is 0.
2 Its{term} is a group and the minimum part of the effective total range of that group, as defined byEffective Total Range (all and sequence) (§3.8.6) (if the group is all or sequence) orEffective Total Range (choice) (§3.8.6) (if it is choice), is 0.
3.10 Wildcards3.10.1The Wildcard Schema Component
3.10.2XML Representation of Wildcard Schema Components
3.10.3Constraints on XML Representations of Wildcards
3.10.4Wildcard Validation Rules
3.10.5Wildcard Information Set Contributions
3.10.6Constraints on Wildcard Schema Components
In order to exploit the full potential for extensibility offered by XML plus namespaces, more provision is needed than DTDs allow for targeted flexibility in content models and attribute declarations. A wildcard provides for·validation· of attribute and element information items dependent on their namespace name, but independently of their local name.
Example
XML representations of the four basic types of wildcard, plus one attribute wildcard.
3.10.1 The Wildcard Schema Component
The wildcard schema component has the following properties:
Schema Component: Wildcard
One of any; a pair of not and a namespace name or·absent·; or a set whose members are either namespace names or·absent·.One of skip, lax or strict.Optional. An annotation.
{namespace constraint} provides for·validation· of attribute and element items that:
(any) have any namespace or are not namespace qualified; (not and a namespace name) have any namespace other than the specified namespace name, or are not namespace qualified; (not and·absent·) are namespace qualified; (a set whose members are either namespace names or·absent·) have any of the specified namespaces and/or, if·absent· is included in the set, are unqualified.
{process contents} controls the impact on·assessment· of the information items allowed by wildcards, as follows:
strictThere must be a top-level declaration for the item available, or the item must have an xsi:type, and the item must be·valid· as appropriate.skipNo constraints at all: the item must simply be well-formed XML.laxIf the item, or any items among its[children] if it‘s an element information item, has a uniquely determined declaration available, it must be·valid· with respect to that definition, that is,·validate· where you can, don‘t worry when you can‘t.
SeeAnnotations (§3.13) for information on the role of the{annotation} property.
3.10.2 XML Representation of Wildcard Schema Components
The XML representation for a wildcard schema component is an
XML Representation Summary: any Element Information Item
id =ID
maxOccurs = (nonNegativeInteger | unbounded) : 1
minOccurs =nonNegativeInteger : 1
namespace = ((##any | ##other) | List of (anyURI | (##targetNamespace | ##local)) ) : ##any
processContents = (lax | skip | strict) : strict
{any attributes with non-schema namespace . . .}>
Content: (annotation?)
A particle containing a wildcard, with properties as follows (unless minOccurs=maxOccurs=0, in which case the item corresponds to no component at all):
Particle Schema Component
Property Representation
{min occurs} The·actual value· of the minOccurs[attribute], if present, otherwise 1.
{max occurs} unbounded, if the maxOccurs[attribute] equals unbounded, otherwise the·actual value· of the maxOccurs[attribute], if present, otherwise 1.
{term} A wildcard as given below:
Wildcard Schema Component
Property Representation
{namespace constraint} Dependent on the·actual value· of the namespace[attribute]: if absent, then any, otherwise as follows: ##any any ##other a pair of not and the·actual value· of the targetNamespace[attribute] of the
2 if one such substring is ##local, the corresponding member is·absent·.
{process contents} The·actual value· of the processContents[attribute], if present, otherwise strict.
{annotation} The annotation corresponding to the
Wildcards are subject to the same ambiguity constraints (Unique Particle Attribution (§3.8.6)) as other content model particles: If an instance element could match either an explicit particle and a wildcard, or one of two wildcards, within the content model of a type, that model is in error.
3.10.3 Constraints on XML Representations of Wildcards
Schema Representation Constraint: Wildcard Representation OK
In addition to the conditions imposed on
3.10.4 Wildcard Validation Rules
Validation Rule: Item Valid (Wildcard)
For an element or attribute information item to be locally·valid· with respect to a wildcard constraint its[namespace name] must be·valid· with respect to the wildcard constraint, as defined inWildcard allows Namespace Name (§3.10.4).
When this constraint applies the appropriate case among the following must be true:1 If{process contents} is lax, then the item has no·context-determined declaration· with respect toAssessment Outcome (Element) (§3.3.5),Schema-Validity Assessment (Element) (§3.3.4) andSchema-Validity Assessment (Attribute) (§3.2.4).
2 If{process contents} is strict, then the item‘s·context-determined declaration· is mustFind.
3 If{process contents} is skip, then the item‘s·context-determined declaration· is skip.
Validation Rule: Wildcard allows Namespace Name
For a value which is either a namespace name or·absent· to be·valid· with respect to a wildcard constraint (the value of a{namespace constraint}) one of the following must be true:1 The constraint must be any.
2 All of the following must be true:2.1 The constraint is a pair of not and a namespace name or·absent· (call this the namespace test).
2.2 The value must not be identical to the·namespace test·.
2.3 The value must not be·absent·.
3 The constraint is a set, and the value is identical to one of the members of the set.
3.10.5 Wildcard Information Set Contributions
None as such.
3.10.6 Constraints on Wildcard Schema Components
All wildcards (seeWildcards (§3.10)) must satisfy the following constraint.
Schema Component Constraint: Wildcard Properties Correct
The values of the properties of a wildcard must be as described in the property tableau inThe Wildcard Schema Component (§3.10.1), modulo the impact ofMissing Sub-components (§5.3).
The following constraints define a relation appealed to elsewhere in this specification.
Schema Component Constraint: Wildcard Subset
For a namespace constraint (call it sub) to be an intensional subset of another namespace constraint (call it super) one of the following must be true:1 super must be any.
2 All of the following must be true:2.1 sub must be a pair of not and a namespace name or·absent·.
2.2 super must be a pair of not and the same value.
3 All of the following must be true:3.1 sub must be a set whose members are either namespace names or·absent·.
3.2 One of the following must be true:3.2.1 super must be the same set or a superset thereof.
3.2.2 super must be a pair of not and a namespace name or·absent· and that value must not be in sub‘s set.
Schema Component Constraint: Attribute Wildcard Union
For a wildcard‘s{namespace constraint} value to be the intensional union of two other such values (call them O1 and O2): the appropriate case among the following must be true:1 If O1 and O2 are the same value, then that value must be the value.
2 If either O1 or O2 is any, then any must be the value.
3 If both O1 and O2 are sets of (namespace names or·absent·), then the union of those sets must be the value.
4 If the two are negations of different namespace names, then the intersection is not expressible.
5 If either O1 or O2 is a pair of not and a namespace name and the other is a set of (namespace names or·absent·), then The appropriate case among the following must be true:5.1 If the set includes the negated namespace name, then any must be the value.
5.2 If the set does not include the negated namespace name, then whichever of O1 or O2 is a pair of not and a namespace name must be the value.
In the case where there are more than two values, the intensional intersection is determined by identifying the intensional intersection of two of the values as above, then the intensional intersection of that value with the third (providing the first intersection was expressible), and so on as required.
Schema Component Constraint: Attribute Wildcard Intersection
For a wildcard‘s{namespace constraint} value to be the intensional intersection of two other such values (call them O1 and O2): the appropriate case among the following must be true:1 If O1 and O2 are the same value, then that value must be the value.
2 If either O1 or O2 is any, then the other must be the value.
3 If either O1 or O2 is a pair of not and a namespace name and the other is a set of (namespace names or·absent·), then that set, minus the negated namespace name if it was in the set, must be the value.
4 If both O1 and O2 are sets of (namespace names or·absent·), then the intersection of those sets must be the value.
5 If the two are negations of different namespace names, then the intersection is not expressible.
In the case where there are more than two values, the intensional intersection is determined by identifying the intensional intersection of two of the values as above, then the intensional intersection of that value with the third (providing the first intersection was expressible), and so on as required.
3.11 Identity-constraint Definitions3.11.1The Identity-constraint Definition Schema Component
3.11.2XML Representation of Identity-constraint Definition Schema Components
3.11.3Constraints on XML Representations of Identity-constraint Definitions
3.11.4Identity-constraint Definition Validation Rules
3.11.5Identity-constraint Definition Information Set Contributions
3.11.6Constraints on Identity-constraint Definition Schema Components
Identity-constraint definition components provide for uniqueness and reference constraints with respect to the contents of multiple elements and attributes.
Example
XML representations for the three kinds of identity-constraint definitions.
3.11.1 The Identity-constraint Definition Schema Component
The identity-constraint definition schema component has the following properties:
Schema Component: Identity-constraint Definition
An NCName as defined by[XML-Namespaces].Either·absent· or a namespace name, as defined in[XML-Namespaces].One of key, keyref or unique.A restricted XPath ([XPath]) expression.A non-empty list of restricted XPath ([XPath]) expressions.Required if{identity-constraint category} is keyref, forbidden otherwise. An identity-constraint definition with{identity-constraint category} equal to key or unique.Optional. An annotation.
Identity-constraint definitions are identified by their{name} and{target namespace}; Identity-constraint definition identities must be unique within an·XML Schema·. SeeReferences to schema components across namespaces (§4.2.3) for the use of component identifiers when importing one schema into another.
Informally,{identity-constraint category} identifies the Identity-constraint definition as playing one of three roles:
(unique) the Identity-constraint definition asserts uniqueness, with respect to the content identified by{selector}, of the tuples resulting from evaluation of the{fields} XPath expression(s). (key) the Identity-constraint definition asserts uniqueness as for unique. key further asserts that all selected content actually has such tuples. (keyref) the Identity-constraint definition asserts a correspondence, with respect to the content identified by{selector}, of the tuples resulting from evaluation of the{fields} XPath expression(s), with those of the{referenced key}.
These constraints are specified along side the specification of types for the attributes and elements involved, i.e. something declared as of type integer may also serve as a key. Each constraint declaration has a name, which exists in a single symbol space for constraints. The equality and inequality conditions appealed to in checking these constraints apply to the value of the fields selected, so that for example 3.0 and 3 would be conflicting keys if they were both number, but non-conflicting if they were both strings, or one was a string and one a number. Values of differing type can only be equal if one type is derived from the other, and the value is in the value space of both.
Overall the augmentations to XML‘s ID/IDREF mechanism are:
Functioning as a part of an identity-constraint is in addition to, not instead of, having a type; Not just attribute values, but also element content and combinations of values and content can be declared to be unique; Identity-constraints are specified to hold within the scope of particular elements; (Combinations of) attribute values and/or element content can be declared to be keys, that is, not only unique, but always present and non-nillable; The comparison between keyref{fields} and key or unique{fields} is by value equality, not by string equality.
{selector} specifies a restricted XPath ([XPath]) expression relative to instances of the element being declared. This must identify a node set of subordinate elements (i.e. contained within the declared element) to which the constraint applies.
{fields} specifies XPath expressions relative to each element selected by a{selector}. This must identify a single node (element or attribute) whose content or value, which must be of a simple type, is used in the constraint. It is possible to specify an ordered list of{fields}s, to cater to multi-field keys, keyrefs, and uniqueness constraints.
In order to reduce the burden on implementers, in particular implementers of streaming processors, only restricted subsets of XPath expressions are allowed in{selector} and{fields}. The details are given inConstraints on Identity-constraint Definition Schema Components (§3.11.6).
NOTE: Provision for multi-field keys etc. goes beyond what is supported by xsl:key.
SeeAnnotations (§3.13) for information on the role of the{annotation} property.
3.11.2 XML Representation of Identity-constraint Definition Schema Components
The XML representation for an identity-constraint definition schema component is either a
XML Representation Summary: unique Element Information Item
id =ID
name =NCName
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (selector,field+))
id =ID
name =NCName
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (selector,field+))
id =ID
name =NCName
refer =QName
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (selector,field+))
id =ID
xpath = a subset of XPath expression, see below
{any attributes with non-schema namespace . . .}>
Content: (annotation?)
id =ID
xpath = a subset of XPath expression, see below
{any attributes with non-schema namespace . . .}>
Content: (annotation?)
Identity-constraint Definition Schema Component
Property Representation
{name} The·actual value· of the name[attribute]
{target namespace} The·actual value· of the targetNamespace[attribute] of the parent schema element information item.
{identity-constraint category} One of key, keyref or unique, depending on the item.
{selector} A restricted XPath expression corresponding to the·actual value· of the xpath[attribute] of the
{fields} A sequence of XPath expressions, corresponding to the·actual value·s of the xpath[attribute]s of the
{referenced key} If the item is a
{annotation} The annotation corresponding to the
Example
A state element is defined, which contains a code child and some vehicle and person children. A vehicle in turn has a plateNumber attribute, which is an integer, and a state attribute. State‘s codes are a key for them within the document. Vehicle‘s plateNumbers are a key for them within states, and state and plateNumber is asserted to be a key for vehicle within the document as a whole. Furthermore, a person element has an empty car child, with regState and regPlate attributes, which are then asserted together to refer to vehicles via the carRef constraint. The requirement that a vehicle‘s state match its containing state‘s code is not expressed here.
3.11.3 Constraints on XML Representations of Identity-constraint Definitions
Schema Representation Constraint: Identity-constraint Definition Representation OK
In addition to the conditions imposed on
3.11.4 Identity-constraint Definition Validation Rules
Validation Rule: Identity-constraint Satisfied
For an element information item to be locally·valid· with respect to an identity-constraint all of the following must be true:1 The{selector}, with the element information item as the context node, evaluates to a node-set (as defined in[XPath]). Call this the target node set.
2 Each node in the·target node set· is an element node among the descendants of the context node.
3 For each node in the·target node set· all of the{fields}, with that node as the context node, evaluate to either an empty node-set or a node-set with exactly one member, which must have a simple type. Call the sequence of the type-determined values (as defined in[XML Schemas: Datatypes]) of the [schema normalized value] of the element and/or attribute information items in those node-sets in order the key-sequence of the node.
4 Call the subset of the·target node set· for which all the{fields} evaluate to a node-set with exactly one member which is an element or attribute node with a simple type the qualified node set. The appropriate case among the following must be true:4.1If the{identity-constraint category} is unique, then no two members of the·qualified node set· have·key-sequences· whose members are pairwise equal, as defined byEqual in[XML Schemas: Datatypes].
4.2If the{identity-constraint category} is key, then all of the following must be true:4.2.1 The·target node set· and the·qualified node set· are equal, that is, every member of the·target node set· is also a member of the·qualified node set· and vice versa.
4.2.2 No two members of the·qualified node set· have·key-sequences· whose members are pairwise equal, as defined byEqual in[XML Schemas: Datatypes].
4.2.3No element member of the·key-sequence· of any member of the·qualified node set· was assessed as·valid· by reference to an element declaration whose{nillable} is true.
4.3 If the{identity-constraint category} is keyref, then for each member of the·qualified node set· (call this the keyref member), there must be a·node table· associated with the{referenced key} in the[identity-constraint table] of the element information item (seeIdentity-constraint Table (§3.11.5), which must be understood as logically prior to this clause of this constraint, below) and there must be an entry in that table whose·key-sequence· is equal to the keyref member‘s·key-sequence· member for member, as defined byEqual in[XML Schemas: Datatypes].
NOTE: The use of [schema normalized value] in the definition of·key sequence· above means that default or fixed value constraints may play a part in·key sequence·s.
NOTE: Although this specification defines a post-schema-validation infoset contribution which would enable schema-aware processors to implement clause4.2.3 above (Element Declaration (§3.3.5)), processors are not required to provide it. This clause can be read as if in the absence of this infoset contribution, the value of the relevant{nillable} property must be available.
3.11.5 Identity-constraint Definition Information Set Contributions
Schema Information Set Contribution: Identity-constraint Table
An eligible identity-constraint of an element information item is one such that clause4.1 or clause4.2 ofIdentity-constraint Satisfied (§3.11.4) is satisfied with respect to that item and that constraint, or such that any of the element information item[children] of that item have an[identity-constraint table] property whose value has an entry for that constraint.
A node table is a set of pairs each consisting of a·key-sequence· and an element node.
Whenever an element information item has one or more·eligible identity-constraints·, in the post-schema-validation infoset that element information item has a property as follows:PSVI Contributions for element information items
one Identity-constraint Binding information item for each·eligible identity-constraint·, with properties as follows:PSVI Contributions for Identity-constraint Binding information items
The·eligible identity-constraint·.A·node table· with one entry for every·key-sequence· (call it k) and node (call it n) such that one of the following must be true:1There is an entry in one of the·node tables· associated with the[definition] in an Identity-constraint Binding information item in at least one of the[identity-constraint table]s of the element information item[children] of the element information item whose·key-sequence· is k and whose node is n;
2 n appears with·key-sequence· k in the·qualified node set· for the[definition].
provided no two entries have the same·key-sequence· but distinct nodes. Potential conflicts are resolved by not including any conflicting entries which would have owed their inclusion to clause1 above. Note that if all the conflicting entries arose under clause1 above, this means no entry at all will appear for the offending·key-sequence·.
NOTE: The complexity of the above arises from the fact that keyref identity-constraints may be defined on domains distinct from the embedded domain of the identity-constraint they reference, or the domains may be the same but self-embedding at some depth. In either case the·node table· for the referenced identity-constraint needs to propagate upwards, with conflict resolution.
The Identity-constraint Binding information item, unlike others in this specification, is essentially an internal bookkeeping mechanism. It is introduced to support the definition ofIdentity-constraint Satisfied (§3.11.4) above. Accordingly, conformant processors may, but are not required to, expose them via[identity-constraint table] properties in the post-schema-validation infoset. In other words, the above constraints may be read as saying·validation· of identity-constraints proceeds as if such infoset items existed.
3.11.6 Constraints on Identity-constraint Definition Schema Components
All identity-constraint definitions (seeIdentity-constraint Definitions (§3.11)) must satisfy the following constraint.
Schema Component Constraint: Identity-constraint Definition Properties Correct
All of the following must be true:1 The values of the properties of an identity-constraint definition must be as described in the property tableau inThe Identity-constraint Definition Schema Component (§3.11.1), modulo the impact ofMissing Sub-components (§5.3).
2 If the{identity-constraint category} is keyref, the cardinality of the{fields} must equal that of the{fields} of the{referenced key}.
Schema Component Constraint: Selector Value OK
All of the following must be true:1 The{selector} must be a valid XPath expression, as defined in[XPath].
2 One of the following must be true:2.1 It must conform to the following extended BNF: Selector XPath expressions
[1] Selector ::= Path ( ‘|‘Path )*
[2] Path ::= (‘.//‘)?Step ( ‘/‘Step )*
[3] Step ::= ‘.‘ |NameTest
[4] NameTest ::= QName | ‘*‘ |NCName ‘:‘ ‘*‘
2.2 It must be an XPath expression involving the child axis whose abbreviated form is as given above.
Schema Component Constraint: Fields Value OK
All of the following must be true:1 Each member of the{fields} must be a valid XPath expression, as defined in[XPath].
2 One of the following must be true:2.1 It must conform to the extended BNF given above forSelector, with the following modification: Path in Field XPath expressions
[5] Path ::= (‘.//‘)? (Step ‘/‘ )* (Step | ‘@‘NameTest )
This production differs from the one above in allowing the final step to match an attribute node.
2.2 It must be an XPath expression involving the child and/or attribute axes whose abbreviated form is as given above.
3.12 Notation Declarations3.12.1The Notation Declaration Schema Component
3.12.2XML Representation of Notation Declaration Schema Components
3.12.3Constraints on XML Representations of Notation Declarations
3.12.4Notation Declaration Validation Rules
3.12.5Notation Declaration Information Set Contributions
3.12.6Constraints on Notation Declaration Schema Components
Notation declarations reconstruct XML 1.0 NOTATION declarations.
Example
The XML representation of a notation declaration.
3.12.1 The Notation Declaration Schema Component
The notation declaration schema component has the following properties:
Schema Component: Notation Declaration
An NCName as defined by[XML-Namespaces].Either·absent· or a namespace name, as defined in[XML-Namespaces].Optional if{public identifier} is present. A URI reference.Optional if{system identifier} is present. A public identifier, as defined in[XML 1.0 (Second Edition)].Optional. An annotation.
Notation declarations do not participate in·validation· as such. They are referenced in the course of·validating· strings as members of theNOTATION simple type.
SeeAnnotations (§3.13) for information on the role of the{annotation} property.
3.12.2 XML Representation of Notation Declaration Schema Components
The XML representation for a notation declaration schema component is a
XML Representation Summary: notation Element Information Item
id =ID
name =NCName
public =anyURI
system =anyURI
{any attributes with non-schema namespace . . .}>
Content: (annotation?)
Notation Declaration Schema Component
Property Representation
{name} The·actual value· of the name[attribute]
{target namespace} The·actual value· of the targetNamespace[attribute] of the parent schema element information item.
{system identifier} The·actual value· of the system[attribute], if present, otherwise·absent·.
{public identifier} The·actual value· of the public[attribute]
{annotation} The annotation corresponding to the
Example
3.12.3 Constraints on XML Representations of Notation Declarations
Schema Representation Constraint: Notation Definition Representation OK
In addition to the conditions imposed on
3.12.4 Notation Declaration Validation Rules
None as such.
3.12.5 Notation Declaration Information Set Contributions
Schema Information Set Contribution: Validated with Notation
Whenever an attribute information item is·valid· with respect to aNOTATION, in the post-schema-validation infoset its parent element information item either has a property as follows:PSVI Contributions for element information items
An·item isomorphic· to the notation declaration whose{name} and{target namespace} match the·local name· and·namespace name· (as defined inQName Interpretation (§3.15.3)) of the attribute item‘s·actual value·
or has a pair of properties as follows:PSVI Contributions for element information items
The value of the{system identifier} of that notation declaration.The value of the{public identifier} of that notation declaration.
NOTE: For compatibility, only one such attribute should appear on any given element. If more than one such attribute does appear, which one supplies the infoset property or properties above is not defined.
3.12.6 Constraints on Notation Declaration Schema Components
All notation declarations (seeNotation Declarations (§3.12)) must satisfy the following constraint.
Schema Component Constraint: Notation Declaration Correct
The values of the properties of a notation declaration must be as described in the property tableau inThe Notation Declaration Schema Component (§3.12.1), modulo the impact ofMissing Sub-components (§5.3).
3.13 Annotations3.13.1The Annotation Schema Component
3.13.2XML Representation of Annotation Schema Components
3.13.3Constraints on XML Representations of Annotations
3.13.4Annotation Validation Rules
3.13.5Annotation Information Set Contributions
3.13.6Constraints on Annotation Schema Components
Annotations provide for human- and machine-targeted annotations of schema components.
Example
XML representations of three kinds of annotation.
3.13.1 The Annotation Schema Component
The annotation schema component has the following properties:
Schema Component: Annotation
A sequence of element information items.A sequence of element information items.A sequence of attribute information items.
{user information} is intended for human consumption,{application information} for automatic processing. In both cases, provision is made for an optional URI reference to supplement the local information, as the value of the source attribute of the respective element information items.·Validation· does not involve dereferencing these URIs, when present. In the case of{user information}, indication should be given as to the identity of the (human) language used in the contents, using the xml:lang attribute.
{attributes} ensures that when schema authors take advantage of the provision for adding attributes from namespaces other than the XML Schema namespace to schema documents, they are available within the components corresponding to the element items where such attributes appear.
Annotations do not participate in·validation· as such. Provided an annotation itself satisfies all relevant·Schema Component Constraints· it cannot affect the·validation· of element information items.
3.13.2 XML Representation of Annotation Schema Components
Annotation of schemas and schema components, with material for human or computer consumption, is provided for by allowing application information and human information at the beginning of most major schema elements, and anywhere at the top level of schemas. The XML representation for an annotation schema component is an
XML Representation Summary: annotation Element Information Item
id =ID
{any attributes with non-schema namespace . . .}>
Content: (appinfo |documentation)*
source =anyURI>
Content: ({any})*
source =anyURI
xml:lang =language>
Content: ({any})*
Annotation Schema Component
Property Representation
{application information} A sequence of the
{user information} A sequence of the
{attributes} A sequence of attribute information items, namely those allowed by the attribute wildcard in the type definition for the
The annotation component corresponding to the
3.13.3 Constraints on XML Representations of Annotations
Schema Representation Constraint: Annotation Definition Representation OK
In addition to the conditions imposed on
3.13.4 Annotation Validation Rules
None as such.
3.13.5 Annotation Information Set Contributions
None as such: the addition of annotations to the post-schema-validation infoset is covered by the post-schema-validation infoset contributions of the enclosing components.
3.13.6 Constraints on Annotation Schema Components
All annotations (seeAnnotations (§3.13)) must satisfy the following constraint.
Schema Component Constraint: Annotation Correct
The values of the properties of an annotation must be as described in the property tableau inThe Annotation Schema Component (§3.13.1), modulo the impact ofMissing Sub-components (§5.3).
3.14 Simple Type Definitions3.14.1(non-normative) The Simple Type Definition Schema Component
3.14.2(non-normative) XML Representation of Simple Type Definition Schema Components
3.14.3(non-normative) Constraints on XML Representations of Simple Type Definitions
3.14.4Simple Type Definition Validation Rules
3.14.5Simple Type Definition Information Set Contributions
3.14.6Constraints on Simple Type Definition Schema Components
3.14.7Built-in Simple Type Definition
NOTE: This section consists of a combination of non-normative versions of normative material from[XML Schemas: Datatypes], for local cross-reference purposes, and normative material relating to the interface between schema components defined in this specification and the simple type definition component.
Simple type definitions provide for constraining character information item[children] of element and attribute information items.
Example
The XML representation of a simple type definition.
3.14.1 (non-normative) The Simple Type Definition Schema Component
The simple type definition schema component has the following properties:
Schema Component: Simple Type Definition
Optional. An NCName as defined by[XML-Namespaces].Either·absent· or a namespace name, as defined in[XML-Namespaces].A simple type definition, which may be the·simple ur-type definition·.A set of constraining facets.A set of fundamental facets.A subset of {extension, list, restriction, union}.One of {atomic, list, union}. Depending on the value of{variety}, further properties are defined as follows:atomicA built-in primitive simple type definition (or the·simple ur-type definition·).
listA simple type definition.
unionA non-empty sequence of simple type definitions.
Optional. An annotation.
Simple types are identified by their{name} and{target namespace}. Except for anonymous simple types (those with no{name}), since type definitions (i.e. both simple and complex type definitions taken together) must be uniquely identified within an·XML Schema·, no simple type definition can have the same name as another simple or complex type definition. Simple type{name}s and{target namespace}s are provided for reference from instances (seexsi:type (§2.6.1)), and for use in the XML representation of schema components (specifically in
NOTE: The{name} of a simple type is not ipso facto the[(local) name] of the element or attribute information items·validated· by that definition. The connection between a name and a type definition is described inElement Declarations (§3.3) andAttribute Declarations (§3.2).
A simple type definition with an empty specification for{final} can be used as the{base type definition} for other types derived by either of extension or restriction, or as the{item type definition} in the definition of a list, or in the{member type definitions} of a union; the explicit values extension, restriction, list and union prevent further derivations by extension (to yield a complex type) and restriction (to yield a simple type) and use in constructing lists and unions respectively.
{variety} determines whether the simple type corresponds to an atomic, list or union type as defined by[XML Schemas: Datatypes].
As described inType Definition Hierarchy (§2.2.1.1), every simple type definition is a·restriction· of some other simple type (the{base type definition}), which is the simple·ur-type definition· if and only if the type definition in question is one of the built-in primitive datatypes, or a list or union type definition. Each atomic type is ultimately a restriction of exactly one such built-in simple{primitive type definition}.
{facets} for each simple type definition are selected from those defined in[XML Schemas: Datatypes]. For atomic definitions, these are restricted to those appropriate for the corresponding{primitive type definition}. Therefore, the value space and lexical space (i.e. what is·validated· by any atomic simple type) is determined by the pair ({primitive type definition},{facets}).
As specified in[XML Schemas: Datatypes], list simple type definitions·validate· space separated tokens, each of which conforms to a specified simple type definition, the{item type definition}. The item type specified must not itself be a list type, and must be one of the types identified in[XML Schemas: Datatypes] as a suitable item type for a list simple type. In this case the{facets} apply to the list itself, and are restricted to those appropriate for lists.
A union simple type definition·validates· strings which satisfy at least one of its{member type definitions}. As in the case of list, the{facets} apply to the union itself, and are restricted to those appropriate for unions.
As discussed inType Definition Hierarchy (§2.2.1.1), the·ur-type definition· functions as a simple type when used as the·base type definition· for the built-in primitive datatypes and for list and union type definitions. It is considered to have an unconstrained lexical space, and a value space consisting of the union of the value spaces of all the built-in primitive datatypes and the set of all lists of all members of the value spaces of all the built-in primitive datatypes.
The simple·ur-type definition· must not be named as the·base type definition· of any user-defined simple types: as it has no constraining facets, this would be incoherent.
SeeAnnotations (§3.13) for information on the role of the{annotation} property.
3.14.2 (non-normative) XML Representation of Simple Type Definition Schema Components
NOTE: This section reproduces a version of material from[XML Schemas: Datatypes], for local cross-reference purposes. XML Representation Summary: simpleType Element Information Item
final = (#all | (list | union | restriction))
id =ID
name =NCName
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (restriction |list |union))
base =QName
id =ID
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (simpleType?, (minExclusive |minInclusive |maxExclusive |maxInclusive |totalDigits |fractionDigits |length |minLength |maxLength |enumeration |whiteSpace |pattern)*))
id =ID
itemType =QName
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (simpleType?))
id =ID
memberTypes = List ofQName
{any attributes with non-schema namespace . . .}>
Content: (annotation?, (simpleType*))
Simple Type Definition Schema Component
Property Representation
{name} The·actual value· of the name[attribute] if present, otherwise·absent·.
{target namespace} The·actual value· of the targetNamespace[attribute] of the
{base type definition} The appropriate case among the following: 1 If the
2 If the
- or
{final} As for the{prohibited substitutions} property of complex type definitions, but using the final and finalDefault[attributes] in place of the block and blockDefault[attributes] and with the relevant set being {extension, restriction, list, union}.
{variety} If the
- alternative is chosen, then list, otherwise if the
If the{variety} is atomic, the following additional property mappings also apply:
Atomic Simple Type Definition Schema Component
Property Representation
{primitive type definition} The built-in primitive type definition from which the{base type definition} is derived.
{facets} A set of facet components·constituting a restriction· of the{facets} of the{base type definition} with respect to a set of facet components corresponding to the appropriate element information items among the[children] of
If the{variety} is list, the following additional property mappings also apply:
List Simple Type Definition Schema Component
Property Representation
{item type definition} The appropriate case among the following: 1 If the
- alternative is chosen, then the type definition·resolved· to by the·actual value· of the itemType[attribute] of
- , if present, otherwise the type definition corresponding to the
- .
2 If the
{facets} If the
If the{variety} is union, the following additional property mappings also apply:
Union Simple Type Definition Schema Component
Property Representation
{member type definitions} The appropriate case among the following: 1 If the
2 If the
{facets} If the
3.14.3 (non-normative) Constraints on XML Representations of Simple Type Definitions
Schema Representation Constraint: Simple Type Definition Representation OK
In addition to the conditions imposed on
2 If the
3 If the
- alternative is chosen, either it must have an itemType[attribute] or a
4 Circular union type definition is disallowed. That is, if the
Schema Representation Constraint: Simple Type Restriction (Facets)
For a simple type definition (call it R) to restrict another simple type definition (call it B) with a set of facets (call this S) all of the following must be true:1 The{variety} and{primitive type definition} of R are the same as those of B.
2The{facets} of R are the union of S and the{facets} of B, eliminating duplicates. To eliminate duplicates, when a facet of the same kind occurs in both S and the{facets} of B, the one in the{facets} of B is not included, with the exception ofenumeration andpattern facets, for which multiple occurrences with distinct values are allowed.
If clause2 above holds, the{facets} of R constitute a restriction of the{facets} of B with respect to S.
3.14.4 Simple Type Definition Validation Rules
Validation Rule: String Valid
A string is locally·valid· with respect to a simple type definition if it is schema-valid with respect to that definition as defined byDatatype Valid in[XML Schemas: Datatypes].
3.14.5 Simple Type Definition Information Set Contributions
None as such.
3.14.6 Constraints on Simple Type Definition Schema Components
All simple type definitions (seeSimple Type Definitions (§3.14)) must satisfy the following constraints.
Schema Component Constraint: Simple Type Definition Properties Correct
All of the following must be true:1 The values of the properties of a simple type definition must be as described in the property tableau inDatatype definition, modulo the impact ofMissing Sub-components (§5.3).
2 Circular definitions are disallowed. That is, it must be possible to reach a built-in primitive datatype or the·simple ur-type definition· by repeatedly following the{base type definition}.
3 The{final} of the{base type definition} must not contain restriction.
4 If the{base type definition} is not the·simple ur-type definition·, all of the following must be true:4.1 The definition must be a·valid restriction· as defined inDerivation Valid (Restriction, Simple) (§3.14.6).
4.2 If{variety} is not atomic, then the appropriate case among the following must be true:4.2.1 If the{variety} is list, then the{final} of the{base type definition} must not contain list.
4.2.2 If the{variety} is union, then the{final} of the{base type definition} must not contain union.
Schema Component Constraint: Derivation Valid (Restriction, Simple)
The appropriate case among the following must be true:1 If the{variety} is atomic, then all of the following must be true:1.1 The{base type definition} must be an atomic simple type definition or a built-in primitive datatype.
1.2 The{final} of the{base type definition} must not contain restriction.
1.3 For each facet in the{facets} there must be a facet of the same kind in the{facets} of the{base type definition} of whose {value} the facet in question‘s {value} must be a valid restriction as defined in[XML Schemas: Datatypes].
2 If the{variety} is list, then all of the following must be true:2.1 The{item type definition} must have a{variety} of atomic or union (in which case all the{member type definitions} must be atomic).
2.2 Only length, minLength, maxLength, pattern and enumeration facet components are allowed among the{facets}.
2.3 If the{base type definition} is not the·simple ur-type definition·, then all of the following must be true:2.3.1 The{base type definition} must have a{variety} of list.
2.3.2 The{final} of the{base type definition} must not contain restriction.
2.3.3 for each facet in the{facets} there must be a facet of the same kind in the{facets} of the{base type definition} of whose {value} the facet in question‘s {value} must be a valid restriction as defined in[XML Schemas: Datatypes].
3 If the{variety} is union, then all of the following must be true:3.1 The{member type definitions} must all have{variety} of atomic or list.
3.2 Only pattern and enumeration facet components are allowed among the{facets}.
3.3 If the{base type definition} is not the·simple ur-type definition·, then all of the following must be true:3.3.1 The{base type definition} must have a{variety} of union.
3.3.2 The{final} of the{base type definition} must not contain restriction.
3.3.3 for each facet in the{facets} there must be a facet of the same kind in the{facets} of the{base type definition} of whose {value} the facet in question‘s {value} must be a valid restriction as defined in[XML Schemas: Datatypes].
If this constraintDerivation Valid (Restriction, Simple) (§3.14.6) holds of a simple type definition, it is a valid restriction of its·base type definition·.
The following constraint defines relations appealed to elsewhere in this specification.
Schema Component Constraint: Type Derivation OK (Simple)
For a simple type definition (call it D, for derived) to be validly derived from a simple type definition (call this B, for base) given a subset of {extension, restriction, list, union} (of which only restriction is actually relevant) one of the following must be true:1 They are the same type definition.
2 All of the following must be true:2.1 restriction is not in the subset, or in the{final} of its own{base type definition};
2.2 One of the following must be true:2.2.1 D‘s·base type definition· is B.
2.2.2 D‘s·base type definition· is not the·simple ur-type definition· and is validly derived from B given the subset, as defined by this constraint.
2.2.3 D‘s{variety} is list or union and B is the·simple ur-type definition·.
2.2.4 B‘s{variety} is union and D is validly derived from a type definition in B‘s{member type definitions} given the subset, as defined by this constraint.
3.14.7 Built-in Simple Type Definition
There is a simple type definition nearly equivalent to the simple version of the·ur-type definition· present in every schema by definition. It has the following properties:
Property Value
{name} anySimpleType
{target namespace} http://www.w3.org/2001/XMLSchema
{base type definition}·the ur-type definition·
{final} The empty set
{variety}·absent·
Simple type definitions for all the built-in primitive datatypes, namely string, boolean, float, double, number, dateTime, duration, time, date, gMonth, gMonthDay, gDay, gYear, gYearMonth, hexBinary, base64Binary, anyURI (see thePrimitive Datatypes section of[XML Schemas: Datatypes]), as well as for the simple and complex·ur-type definitions· (as previously described), are present by definition in every schema. All are in the XML Schema{target namespace} (namespace name http://www.w3.org/2001/XMLSchema), have an atomic{variety} with an empty{facets} and the simple·ur-type definition· as their·base type definition· and themselves as{primitive type definition}.
Similarly, simple type definitions for all the built-in derived datatypes (see theDerived Datatypes section of[XML Schemas: Datatypes]) are present by definition in every schema, with properties as specified in[XML Schemas: Datatypes] and as represented in XML inSchema for Schemas (normative) (§A).
3.15 Schemas as a Whole3.15.1The Schema Itself
3.15.2XML Representations of Schemas
3.15.3Constraints on XML Representations of Schemas
3.15.4Validation Rules for Schemas as a Whole
3.15.5Schema Information Set Contributions
3.15.6Constraints on Schemas as a Whole
A schema consists of a set of schema components.
Example
The XML representation of the skeleton of a schema.
3.15.1 The Schema Itself
At the abstract level, the schema itself is just a container for its components.
Schema Component: Schema
A set of named simple and complex type definitions.A set of named (top-level) attribute declarations.A set of named (top-level) element declarations.A set of named attribute group definitions.A set of named model group definitions.A set of notation declarations.A set of annotations.
3.15.2 XML Representations of Schemas
A schema is represented in XML by one or more·schema documents·, that is, one or more
XML Representation Summary: schema Element Information Item
attributeFormDefault = (qualified | unqualified) : unqualified
blockDefault = (#all | List of (extension | restriction | substitution)) : ‘‘
elementFormDefault = (qualified | unqualified) : unqualified
finalDefault = (#all | List of (extension | restriction)) : ‘‘
id =ID
targetNamespace =anyURI
version =token
xml:lang =language
{any attributes with non-schema namespace . . .}>
Content: ((include |import |redefine |annotation)*, (((simpleType |complexType |group |attributeGroup) |element |attribute |notation),annotation*)*)
Schema Schema Component
Property Representation
{type definitions} The simple and complex type definitions corresponding to all the
{attribute declarations} The (top-level) attribute declarations corresponding to all the
{element declarations} The (top-level) element declarations corresponding to all the
{attribute group definitions} The attribute group definitions corresponding to all the
{model group definitions} The model group definitions corresponding to all the
{notation declarations} The notation declarations corresponding to all the
{annotations} The annotations corresponding to all the
Note that none of the attribute information items displayed above correspond directly to properties of schemas. The blockDefault, finalDefault, attributeFormDefault, elementFormDefaultand targetNamespace attributes are appealed to in the sub-sections above, as they provide global information applicable to many representation/component correspondences. The other attributes (id and version) are for user convenience, and this specification defines no semantics for them.
The definition of the schema abstract data model inXML Schema Abstract Data Model (§2.2) makes clear that most components have a {target namespace}. Most components corresponding to representations within a given
Since the empty string is not a legal namespace name, supplying an empty string for targetNamespace is incoherent, and is not the same as not specifying it at all. The appropriate form of schema document corresponding to a·schema· whose components have no{target namespace} is one which has no targetNamespace attribute specified at all.
NOTE: The XML namespaces Recommendation discusses only instance document syntax for elements and attributes; it therefore provides no direct framework for managing the names of type definitions, attribute group definitions, and so on. Nevertheless, the specification applies the target namespace facility uniformly to all schema components, i.e. not only declarations but also definitions have a {target namespace}.
Although the example schema at the beginning of this section might be a complete XML document,
Aside from
3.15.2.1 References to Schema Components
Reference to schema components from a schema document is managed in a uniform way, whether the component corresponds to an element information item from the same schema document or is imported (References to schema components across namespaces (§4.2.3)) from an external schema (which may, but need not, correspond to an actual schema document). The form of all such references is a·QName·.
A QName is a name with an optional namespace qualification, as defined in[XML-Namespaces]. When used in connection with the XML representation of schema components or references to them, this refers to the simple typeQName as defined in[XML Schemas: Datatypes].
An NCName is a name with no colon, as defined in[XML-Namespaces]. When used in connection with the XML representation of schema components in this specification, this refers to the simple typeNCName as defined in[XML Schemas: Datatypes].
In each of the XML representation expositions in the following sections, an attribute is shown as having type QName if and only if it is interpreted as referencing a schema component.
Example
The first of these is most probably a local reference, i.e. a reference to a type definition corresponding to a
3.15.2.2 References to Schema Components from Elsewhere
The names of schema components such as type definitions and element declarations are not of typeID: they are not unique within a schema, just within a symbol space. This means that simple fragment identifiers will not always work to reference schema components from outside the context of schema documents.
There is currently no provision in the definition of the interpretation of fragment identifiers for the text/xml MIME type, which is the MIME type for schemas, for referencing schema components as such. However,[XPointer] provides a mechanism which maps well onto the notion of symbol spaces as it is reflected in the XML representation of schema components. A fragment identifier of the form #xpointer(xs:schema/xs:element[@name="person"]) will uniquely identify the representation of a top-level element declaration with name person, and similar fragment identifiers can obviously be constructed for the other global symbol spaces.
Short-form fragment identifiers may also be used in some cases, that is when a DTD or XML Schema is available for the schema in question, and the provision of an id attribute for the representations of all primary and secondary schema components, which is of typeID, has been exploited.
It is a matter for applications to specify whether they interpret document-level references of either of the above varieties as being to the relevant element information item (i.e. without special recognition of the relation of schema documents to schema components) or as being to the corresponding schema component.
3.15.3 Constraints on XML Representations of Schemas
Schema Representation Constraint: QName Interpretation
Where the type of an attribute information item in a document involved in·validation· is identified as·QName·, its·actual value· is composed of a local name and a namespace name. Its·actual value· is determined based on its·normalized value· and the containing element information item‘s[in-scope namespaces] following[XML-Namespaces]:
The appropriate case among the following must be true:1 If its·normalized value· is prefixed, then all of the following must be true:1.1 There must be a namespace in the[in-scope namespaces] whose[prefix] matches the prefix.
1.2 its·namespace name· is the[namespace name] of that namespace.
1.3 Its·local name· is the portion of its·normalized value· after the colon (‘:‘).
2 otherwise (its·normalized value· is unprefixed) all of the following must be true:2.1 its·local name· is its·normalized value·.
2.2 The appropriate case among the following must be true:2.2.1 If there is a namespace in the[in-scope namespaces] whose[prefix] has no value, then its·namespace name· is the[namespace name] of that namespace.
2.2.2 otherwise its·namespace name· is·absent·.
In the absence of the[in-scope namespaces] property in the infoset for the schema document in question, processors must reconstruct equivalent information as necessary, using the[ namespace attributes] of the containing element information item and its ancestors.
Whenever the word resolve in any form is used in this chapter in connection with a·QName· in a schema document, the following definitionQName resolution (Schema Document) (§3.15.3) should be understood:
Schema Representation Constraint: QName resolution (Schema Document)
For a·QName· to resolve to a schema component of a specified kind all of the following must be true:1 That component is a member of the value of the appropriate property of the schema which corresponds to the schema document within which the·QName· appears, that is the appropriate case among the following must be true:1.1 If the kind specified is simple or complex type definition, then the property is the{type definitions}.
1.2 If the kind specified is attribute declaration, then the property is the{attribute declarations}.
1.3 If the kind specified is element declaration, then the property is the{element declarations}.
1.4 If the kind specified is attribute group, then the property is the{attribute group definitions}.
1.5 If the kind specified is model group, then the property is the{model group definitions}.
1.6 If the kind specified is notation declaration, then the property is the{notation declarations}.
2 its {local name} matches the·local name· of the·QName·;
3 its {target namespace} is identical to the·namespace name· of the·QName·;
4 its·namespace name· is either the target namespace of the schema document containing the·QName· or that schema document contains an
3.15.4 Validation Rules for Schemas as a Whole
As the discussion above atSchema Component Details (§3) makes clear, at the level of schema components and·validation·, reference to components by name is normally not involved. In a few cases, however, qualified names appearing in information items being·validated· must be resolved to schema components by such lookup. The following constraint is appealed to in these cases.
Validation Rule: QName resolution (Instance)
A pair of a local name and a namespace name (or·absent·) resolve to a schema component of a specified kind in the context of·validation· by appeal to the appropriate property of the schema being used for the·assessment·. Each such property indexes components by name. The property to use is determined by the kind of component specified, that is, the appropriate case among the following must be true:1 If the kind specified is simple or complex type definition, then the property is the{type definitions}.
2 If the kind specified is attribute declaration, then the property is the{attribute declarations}.
3 If the kind specified is element declaration, then the property is the{element declarations}.
4 If the kind specified is attribute group, then the property is the{attribute group definitions}.
5 If the kind specified is model group, then the property is the{model group definitions}.
6 If the kind specified is notation declaration, then the property is the{notation declarations}.
The component resolved to is the entry in the table whose {local name} matches the local name of the pair and whose {target namespace} is identical to the namespace name of the pair.
3.15.5 Schema Information Set Contributions
Schema Information Set Contribution: Schema Information
Schema components provide a wealth of information about the basis of·assessment·, which may well be of relevance to subsequent processing. Reflecting component structure into a form suitable for inclusion in the post-schema-validation infoset is the way this specification provides for making this information available.
Accordingly, by an item isomorphic to a component is meant an information item whose type is equivalent to the component‘s, with one property per property of the component, with the same name, and value either the same atomic value, or an information item corresponding in the same way to its component value, recursively, as necessary.
Processors must add a property in the post-schema-validation infoset to the element information item at which·assessment· began, as follows:PSVI Contributions for element information items
A set of namespace schema information information items, one for each namespace name which appears as the {target namespace} of any schema component in the schema used for that assessment, and one for·absent· if any schema component in the schema had no {target namespace}. Each namespace schema information information item has the following properties and values:PSVI Contributions for namespace schema information information items
A namespace name or·absent·.A (possibly empty) set of schema component information items, each one an·item isomorphic· to a component whose {target namespace} is the sibling[schema namespace] property above, drawn from the schema used for·assessment·.A (possibly empty) set of schema document information items, with properties and values as follows, for each schema document which contributed components to the schema, and whose targetNamespace matches the sibling[schema namespace] property above (or whose targetNamespace was·absent· but that contributed components to that namespace by being
Either a URI reference, if available, otherwise·absent·A document information item, if available, otherwise·absent·.
The{schema components} property is provided for processors which wish to provide a single access point to the components of the schema which was used during·assessment·. Lightweight processors are free to leave it empty, but if it is provided, it must contain at a minimum all the top-level (i.e. named) components which actually figured in the·assessment·, either directly or (because an anonymous component which figured is contained within) indirectly.
Schema Information Set Contribution: ID/IDREF Table
In the post-schema-validation infoset a set of ID/IDREF binding information items is associated with the·validation root· element information item:PSVI Contributions for element information items
A (possibly empty) set of ID/IDREF binding information items, as specified below.
Let the eligible item set be the set of consisting of every attribute or element information item for which all of the following are true1 its [validation context] is the·validation root·;
2 it was successfully·validated· with respect to an attribute declaration as perAttribute Locally Valid (§3.2.4) or element declaration as perElement Locally Valid (Element) (§3.3.4) (as appropriate) whose attribute{type definition} or element{type definition} (respectively) is the built-inID,IDREF orIDREFS simple type definition or a type derived from one of them.
Then there is one ID/IDREF binding in the[ID/IDREF table] for every distinct string which isone of the following:1 the·actual value· of a member of the·eligible item set· whose type definition is or is derived fromID orIDREF;
2 one of the items in the·actual value· of a member of the·eligible item set· whose type definition is or is derived fromIDREFS.
Each ID/IDREF binding has properties as follows:PSVI Contributions for ID/IDREF binding information items
The string identified above.A set consisting of every element information item for which all of the following are true1 its[validation context] is the·validation root·;
2 it has an attribute information item in its[attributes] or an element information item in its[children] which was·validated· by the built-inID simple type definition or a type derived from it whose [schema normalized value] is the[id] of this ID/IDREF binding.
The net effect of the above is to have one entry for every string used as an id, whether by declaration or by reference, associated with those elements, if any, which actually purport to have that id. SeeValidation Root Valid (ID/IDREF) (§3.3.4) above for the validation rule which actually checks for errors here.NOTE: The ID/IDREF binding information item, unlike most other aspects of this specification, is essentially an internal bookkeeping mechanism. It is introduced to support the definition ofValidation Root Valid (ID/IDREF) (§3.3.4) above. Accordingly, conformant processors may, but are not required to, expose it in the post-schema-validation infoset. In other words, the above constraint may be read as saying·assessment· proceeds as if such an infoset item existed.
3.15.6 Constraints on Schemas as a Whole
All schemas (seeSchemas as a Whole (§3.15)) must satisfy the following constraint.
Schema Component Constraint: Schema Properties Correct
All of the following must be true:1 The values of the properties of a schema must be as described in the property tableau inThe Schema Itself (§3.15.1), modulo the impact ofMissing Sub-components (§5.3);
2Each of the{type definitions},{element declarations},{attribute group definitions},{model group definitions} and{notation declarations} must not contain two or more schema components with the same {name} and {target namespace}.
4 Schemas and Namespaces: Access and Composition
This chapter defines the mechanisms by which this specification establishes the necessary precondition for·assessment·, namely access to one or more schemas. This chapter also sets out in detail the relationship between schemas and namespaces, as well as mechanisms for modularization of schemas, including provision for incorporating definitions and declarations from one schema in another, possibly with modifications.
Conformance (§2.4) describes three levels of conformance for schema processors, andSchemas and Schema-validity Assessment (§5) provides a formal definition of·assessment·. This section sets out in detail the 3-layer architecture implied by the three conformance levels. The layers are:
The·assessment· core, relating schema components and instance information items; Schema representation: the connections between XML representations and schema components, including the relationships between namespaces and schema components; XML Schema web-interoperability guidelines: instance->schema and schema->schema connections for the WWW.
Layer 1 specifies the manner in which a schema composed of schema components can be applied to in the·assessment· of an instance element information item. Layer 2 specifies the use of
4.1 Layer 1: Summary of the Schema-validity Assessment CoreThe fundamental purpose of the·assessment· core is to define·assessment· for a single element information item and its descendants with respect to a complex type definition. All processors are required to implement this core predicate in a manner which conforms exactly to this specification.
·assessment· is defined with reference to an·XML Schema· (note not a·schema document·) which consists of (at a minimum) the set of schema components (definitions and declarations) required for that·assessment·. This is not a circular definition, but rather a post facto observation: no element information item can be fully assessed unless all the components required by any aspect of its (potentially recursive)·assessment· are present in the schema.
As specified above, each schema component is associated directly or indirectly with a target namespace, or explicitly with no namespace. In the case of multi-namespace documents, components for more than one target namespace will co-exist in a schema.
Processors have the option to assemble (and perhaps to optimize or pre-compile) the entire schema prior to the start of an·assessment· episode, or to gather the schema lazily as individual components are required. In all cases it is required that:
The processor succeed in locating the·schema components· transitively required to complete an·assessment· (note that components derived from·schema documents· can be integrated with components obtained through other means); no definition or declaration changes once it has been established; if the processor chooses to acquire declarations and definitions dynamically, that there be no side effects of such dynamic acquisition that would cause the results of·assessment· to differ from that which would have been obtained from the same schema components acquired in bulk.
NOTE: the·assessment· core is defined in terms of schema components at the abstract level, and no mention is made of the schema definition syntax (i.e.
The obligation of a schema-aware processor as far as the·assessment· core is concerned is to implement one or more of the options for·assessment· given below inAssessing Schema-Validity (§5.2). Neither the choice of element information item for that·assessment·, nor which of the means of initiating·assessment· are used, is within the scope of this specification.
Although·assessment· is defined recursively, it is also intended to be implementable in streaming processors. Such processors may choose to incrementally assemble the schema during processing in response, for example, to encountering new namespaces. The implication of the invariants expressed above is that such incremental assembly must result in an·assessment· outcome that is the same as would be given if·assessment· was undertaken again with the final, fully assembled schema.
4.2 Layer 2: Schema Documents, Namespaces and Composition4.2.1Assembling a schema for a single target namespace from multiple schema definition documents
4.2.2Including modified component definitions
4.2.3References to schema components across namespaces
The sub-sections ofSchema Component Details (§3) define an XML representation for type definitions and element declarations and so on, specifying their target namespace and collecting them into schema documents. The two following sections relate to assembling a complete schema for·assessment· from multiple sources. They should not be understood as a form of text substitution, but rather as providing mechanisms for distributed definition of schema components, with appropriate schema-specific semantics.
NOTE: The core·assessment· architecture requires that a complete schema with all the necessary declarations and definitions be available. This may involve resolving both instance->schema and schema->schema references. As observed earlier inConformance (§2.4), the precise mechanisms for resolving such references are expected to evolve over time. In support of such evolution, this specification observes the design principle that references from one schema document to a schema use mechanisms that directly parallel those used to reference a schema from an instance document.NOTE: In the sections below, "schemaLocation" really belongs at layer 3. For convenience, it is documented with the layer 2 mechanisms of import and include, with which it is closely associated.4.2.1 Assembling a schema for a single target namespace from multiple schema definition documents
Schema components for a single target namespace can be assembled from several·schema documents·, that is several
XML Representation Summary: include Element Information Item
id =ID
schemaLocation =anyURI
{any attributes with non-schema namespace . . .}>
Content: (annotation?)
A
The·XML Schema· corresponding to
Schema Representation Constraint: Inclusion Constraints and Semantics
In addition to the conditions imposed on
1.2 It resolves to a
In either case call the
2 One of the following must be true:2.1SII has a targetNamespace[attribute], and its·actual value· is identical to the·actual value· of the targetNamespace[attribute] of SII’ (which must have such an[attribute]).
2.2Neither SII nor SII’ have a targetNamespace[attribute].
2.3SII has no targetNamespace[attribute] (but SII’ does).
3 The appropriate case among the following must be true:3.1 If clause2.1 or clause2.2 above is satisfied, then the schema corresponding to SII’ must include not only definitions or declarations corresponding to the appropriate members of its own[children], but also components identical to all the·schema components· of I.
3.2If clause2.3 above is satisfied, then the schema corresponding to the
3.2.2 The{namespace constraint} of a wildcard, whether negated or not;
It is not an error for the·actual value· of the schemaLocation[attribute] to fail to resolve it all, in which case no corresponding inclusion is performed. It is an error for it to resolve but the rest of clause 1 above to fail to be satisfied. Failure to resolve may well cause less than complete·assessment· outcomes, of course.NOTE: As discussed inMissing Sub-components (§5.3),·QName·s in XML representations may fail to·resolve·, rendering components incomplete and unusable because of missing subcomponents. During schema construction, implementations are likely to retain·QName· values for such references, in case subsequent processing provides a referent.·Absent· target·namespace name·s of such as-yet unresolved reference·QName·s in
NOTE: The above is carefully worded so that multiple
4.2.2 Including modified component definitions
In order to provide some support for evolution and versioning, it is possible to incorporate components corresponding to a schema document with modifications. The modifications have a pervasive impact, that is, only the redefined components are used, even when referenced from other incorporated components, whether redefined themselves or not.
XML Representation Summary: redefine Element Information Item
id =ID
schemaLocation =anyURI
{any attributes with non-schema namespace . . .}>
Content: (annotation | (simpleType |complexType |group |attributeGroup))*
A
The·XML Schema· corresponding to
The definitions within the
Type definitions must use themselves as their base type definition; Attribute group definitions and model group definitions must be supersets or subsets of their original definitions, either by including exactly one reference to themselves or by containing only (possibly restricted) components which appear in a corresponding way in their
Not all the components of the
This mechanism is intended to provide a declarative and modular approach to schema modification, with functionality no different except in scope from what would be achieved by wholesale text copying and redefinition by editing. In particular redefining a type is not guaranteed to be side-effect free: it may have unexpected impacts on other type definitions which are based on the redefined one, even to the extent that some such definitions become ill-formed.
NOTE: The pervasive impact of redefinition reinforces the need for implementations to adopt some form of lazy or ‘just-in-time‘ approach to component construction, which is also called for in order to avoid inappropriate dependencies on the order in which definitions and references appear in (collections of) schema documents. Example
v1.xsd:
The schema corresponding to v2.xsd has everything specified by v1.xsd, with the personName type redefined, as well as everything it specifies itself. According to this schema, elements constrained by the personName type may end with a generation element. This includes not only the author element, but also the addressee element.
Schema Representation Constraint: Redefinition Constraints and Semantics
In addition to the conditions imposed on
2 If the·actual value· of the schemaLocation[attribute] successfully resolves one of the following must be true:2.1 it resolves to (a fragment of) a resource which is an XML document (see clause1.1), which in turn corresponds to a
2.2 It resolves to a
In either case call the
3 One of the following must be true:3.1SII has a targetNamespace[attribute], and its·actual value· is identical to the·actual value· of the targetNamespace[attribute] of SII’ (which must have such an[attribute]).
3.2Neither SII nor SII’ have a targetNamespace[attribute].
3.3SII has no targetNamespace[attribute] (but SII’ does).
4 The appropriate case among the following must be true:4.1 If clause3.1 or clause3.2 above is satisfied, then the schema corresponding to SII’ must include not only definitions or declarations corresponding to the appropriate members of its own[children], but also components identical to all the·schema components· of I, with the exception of those explicitly redefined (seeIndividual Component Redefinition (§4.2.2) below).
4.2 If clause3.3 above is satisfied, then the schema corresponding to SII’ must include not only definitions or declarations corresponding to the appropriate members of its own[children], but also components identical to all the·schema components· of I, with the exception of those explicitly redefined (seeIndividual Component Redefinition (§4.2.2) below), except that anywhere the·absent· target namespace name would have appeared, the·actual value· of the targetNamespace[attribute] of SII’ is used (see clause3.2 inInclusion Constraints and Semantics (§4.2.1) for details).
5 Within the[children], each
6 Within the[children], for each
6.1.2 The·actual value· of both that group‘s minOccurs and maxOccurs[attribute] must be 1 (or·absent·).
6.2 If it has no such self-reference, then all of the following must be true:6.2.1 The·actual value· of its own name attribute plus target namespace must successfully·resolve· to a model group definition in I.
6.2.2 The{model group} of the model group definition which corresponds to it perXML Representation of Model Group Definition Schema Components (§3.7.2) must be a·valid restriction· of the{model group} of that model group definition in I, as defined inParticle Valid (Restriction) (§3.9.6).
7 Within the[children], for each
7.2If it has no such self-reference, then all of the following must be true:7.2.1 The·actual value· of its own name attribute plus target namespace must successfully·resolve· to an attribute group definition in I.
7.2.2 The{attribute uses} and{attribute wildcard} of the attribute group definition which corresponds to it perXML Representation of Attribute Group Definition Schema Components (§3.6.2) must be·valid restrictions· of the{attribute uses} and{attribute wildcard} of that attribute group definition in I, as defined in clause2, clause3 and clause4 ofDerivation Valid (Restriction, Complex) (§3.4.6) (where references to the base type definition are understood as references to the attribute group definition in I).
NOTE: An attribute group restrictively redefined per clause7.2 corresponds to an attribute group whose{attribute uses} consist all and only of those attribute uses corresponding to
Schema Representation Constraint: Individual Component Redefinition
Corresponding to each non-
1.2 One component which corresponds to the information item itself, as defined inSchema Component Details (§3), except that its {base type definition} is the component defined in 1.1 above.
This pairing ensures the coherence constraints on type definitions are respected, while at the same time achieving the desired effect, namely that references to names of redefined components in both the
2 The
In all cases there must be a top-level definition item of the appropriate name and kind in the
NOTE: The above is carefully worded so that multiple equivalent
4.2.3 References to schema components across namespaces
As described inXML Schema Abstract Data Model (§2.2), every top-level schema component is associated with a target namespace (or, explicitly, with none). This section sets out the exact mechanism and syntax in the XML form of schema definition by which a reference to a foreign component is made, that is, a component with a different target namespace from that of the referring component.
Two things are required: not only a means of addressing such foreign components but also a signal to schema-aware processors that a schema document contains such references:
XML Representation Summary: import Element Information Item
id =ID
namespace =anyURI
schemaLocation =anyURI
{any attributes with non-schema namespace . . .}>
Content: (annotation?)
The
The·actual value· of the schemaLocation, if present, gives a hint as to where a serialization of a·schema document· with declarations and definitions for that namespace (or none) may be found. When no schemaLocation[attribute] is present, the schema author is leaving the identification of that schema to the instance, application or user, via the mechanisms described below inLayer 3: Schema Document Access and Web-interoperability (§4.3). When a schemaLocation is present, it must contain a single URI reference which the schema author warrants will resolve to a serialization of a·schema document· containing the component(s) in the
NOTE: Since both the namespace and schemaLocation[attribute] are optional, a bare
The same namespace may be used both for real work, and in the course of defining schema components in terms of foreign components:
The treatment of references as·QNames· implies that since (with the exception of the schema for schemas) the target namespace and the XML Schema namespace differ, without massive redeclaration of the default namespace either internal references to the names being defined in a schema document or the schema declaration and definition elements themselves must be explicitly qualified. This example takes the first option -- most other examples in this specification have taken the second.
Schema Representation Constraint: Import Constraints and Semantics
In addition to the conditions imposed on
1.2 If the namespace[attribute] is not present, then the enclosing
2If the application schema reference strategy using the·actual value·s of the schemaLocation and namespace[attributes], provides a referent, as defined bySchema Document Location Strategy (§4.3.2), one of the following must be true:2.1 The referent is (a fragment of) a resource which is an XML document (see clause1.1), which in turn corresponds to a
2.2 The referent is a
In either case call the
3 The appropriate case among the following must be true:3.1 If there is a namespace[attribute], then its·actual value· must be identical to the·actual value· of the targetNamespace[attribute] of SII.
3.2 If there is no namespace[attribute], then SII must have no targetNamespace[attribute]
It is not an error for the application schema reference strategy to fail. It is an error for it to resolve but the rest of clause2 above to fail to be satisfied. Failure to find a referent may well cause less than complete·assessment· outcomes, of course.
The·schema components· (that is{type definitions},{attribute declarations},{element declarations},{attribute group definitions},{model group definitions},{notation declarations}) of a schema corresponding to a
NOTE: The above is carefully worded so that multiple
4.3 Layer 3: Schema Document Access and Web-interoperability4.3.1Standards for representation of schemas and retrieval of schema documents on the Web
4.3.2How schema definitions are located on the Web
Layers 1 and 2 provide a framework for·assessment· and XML definition of schemas in a broad variety of environments. Over time, a range of standards and conventions may well evolve to support interoperability of XML Schema implementations on the World Wide Web. Layer 3 defines the minimum level of function required of all conformant processors operating on the Web: it is intended that, over time, future standards (e.g. XML Packages) for interoperability on the Web and in other environments can be introduced without the need to republish this specification.
4.3.1 Standards for representation of schemas and retrieval of schema documents on the Web
For interoperability, serialized·schema documents·, like all other Web resources, may be identified by URI and retrieved using the standard mechanisms of the Web (e.g. http, https, etc.) Such documents on the Web must be part of XML documents (see clause1.1), and are represented in the standard XML schema definition form described by layer 2 (that is as
NOTE: there will often be times when a schema document will be a complete XML 1.0 document whose document element is
4.3.2 How schema definitions are located on the Web
As described inLayer 1: Summary of the Schema-validity Assessment Core (§4.1), processors are responsible for providing the schema components (definitions and declarations) needed for·assessment·. This section introduces a set of normative conventions to facilitate interoperability for instance and schema documents retrieved and processed from the Web.
NOTE: As discussed above inLayer 2: Schema Documents, Namespaces and Composition (§4.2), other non-Web mechanisms for delivering schemas for·assessment· may exist, but are outside the scope of this specification.
Processors on the Web are free to undertake·assessment· against arbitrary schemas in any of the ways set out inAssessing Schema-Validity (§5.2). However, it is useful to have a common convention for determining the schema to use. Accordingly, general-purpose schema-aware processors (i.e. those not specialized to one or a fixed set of pre-determined schemas) undertaking·assessment· of a document on the web must behave as follows:
unless directed otherwise by the user,·assessment· is undertaken on the document element information item of the specified document; unless directed otherwise by the user, the processor is required to construct a schema corresponding to a schema document whose targetNamespace is identical to the namespace name, if any, of the element information item on which·assessment· is undertaken.
The composition of the complete schema for use in·assessment· is discussed inLayer 2: Schema Documents, Namespaces and Composition (§4.2) above. The means used to locate appropriate schema document(s) are processor and application dependent, subject to the following requirements:
Schemas are represented on the Web in the form specified above inStandards for representation of schemas and retrieval of schema documents on the Web (§4.3.1); The author of a document uses namespace declarations to indicate the intended interpretation of names appearing therein; there may or may not be a schema retrievable via the namespace name. Accordingly whether a processor‘s default behavior is or is not to attempt such dereferencing, it must always provide for user-directed overriding of that default. NOTE: Experience suggests that it is not in all cases safe or desirable from a performance point of view to dereference namespace names as a matter of course. User community and/or consumer/provider agreements may establish circumstances in which such dereference is a sensible default strategy: this specification allows but does not require particular communities to establish and implement such conventions. Users are always free to supply namespace names as schema location information when dereferencing is desired: see below. On the other hand, in case a document author (human or not) created a document with a particular schema in view, and warrants that some or all of the document is conforms to that schema, the schemaLocation and noNamespaceSchemaLocation[attributes] (in the XML Schema instance namespace, that is, http://www.w3.org/2001/XMLSchema-instance) (hereafter xsi:schemaLocation and xsi:noNamespaceSchemaLocation) are provided. The first records the author‘s warrant with pairs of URI references (one for the namespace name, and one for a hint as to the location of a schema document defining names for that namespace name). The second similarly provides a URI reference as a hint as to the location of a schema document with no targetNamespace[attribute].
Unless directed otherwise, for example by the invoking application or by command line option, processors should attempt to dereference each schema document location URI in the·actual value· of such xsi:schemaLocation and xsi:noNamespaceSchemaLocation[attributes], see details below. xsi:schemaLocation and xsi:noNamespaceSchemaLocation[attributes] can occur on any element. However, it is an error if such an attribute occurs after the first appearance of an element or attribute information item within an element information item initially·validated· whose[namespace name] it addresses. According to the rules ofLayer 1: Summary of the Schema-validity Assessment Core (§4.1), the corresponding schema may be lazily assembled, but is otherwise stable throughout·assessment·. Although schema location attributes can occur on any element, and can be processed incrementally as discovered, their effect is essentially global to the·assessment·. Definitions and declarations remain in effect beyond the scope of the element on which the binding is declared.
Example
Multiple schema bindings can be declared using a single attribute. For example consider a stylesheet:
The namespace names used in schemaLocation can, but need not be identical to those actually qualifying the element within whose start tag it is found or its other attributes. For example, as above, all schema location information can be declared on the document element of a document, if desired, regardless of where the namespaces are actually used.
Schema Representation Constraint: Schema Document Location Strategy
Given a namespace name (or none) and (optionally) a URI reference from xsi:schemaLocation or xsi:noNamespaceSchemaLocation, schema-aware processors may implement any combination of the following strategies, in any order:1 Do nothing, for instance because a schema containing components for the given namespace name is already known to be available, or because it is known in advance that no efforts to locate schema documents will be successful (for example in embedded systems);
2 Based on the location URI, identify an existing schema document, either as a resource which is an XML document or a
3 Based on the namespace name, identify an existing schema document, either as a resource which is an XML document or a
4 Attempt to resolve the location URI, to locate a resource on the web which is or contains or references a
5 Attempt to resolve the namespace name to locate such a resource.
Whenever possible configuration and/or invocation options for selecting and/or ordering the implemented strategies should be provided.
Improved or alternative conventions for Web interoperability can be standardized in the future without reopening this specification. For example, the W3C is currently considering initiatives to standardize the packaging of resources relating to particular documents and/or namespaces: this would be an addition to the mechanisms described here for layer 3. This architecture also facilitates innovation at layer 2: for example, it would be possible in the future to define an additional standard for the representation of schema components which allowed e.g. type definitions to be specified piece by piece, rather than all at once.
5 Schemas and Schema-validity Assessment
The architecture of schema-aware processing allows for a rich characterization of XML documents: schema validity is not a binary predicate.
This specification distinguishes between errors in schema construction and structure, on the one hand, and schema validation outcomes, on the other.
5.1 Errors in Schema Construction and StructureBefore·assessment· can be attempted, a schema is required. Special-purpose applications are free to determine a schema for use in·assessment· by whatever means are appropriate, but general purpose processors should implement the strategy set out inSchema Document Location Strategy (§4.3.2), starting with the namespaces declared in the document whose·assessment· is being undertaken, and the·actual value·s of the xsi:schemaLocation and xsi:noNamespaceSchemaLocation[attributes] thereof, if any, along with an other information about schema identity or schema document location provided by users in application-specific ways, if any.
It is an error if a schema and all the components which are the value of any of its properties, recursively, fail to satisfy all the relevant Constraints on Schemas set out in the last section of each of the subsections ofSchema Component Details (§3).
If a schema is derived from one or more schema documents (that is, one or more
It is an error if any such schema document would not be fully valid with respect to a schema corresponding to theSchema for Schemas (normative) (§A), that is, following schema-validation with such a schema, the
The three cases described above are the only types of error which this specification defines. With respect to the processes of the checking of schema structure and the construction of schemas corresponding to schema documents, this specification imposes no restrictions on processors after an error is detected. However·assessment· with respect to schema-like entities which do not satisfy all the above conditions is incoherent. Accordingly, conformant processors must not attempt to undertake·assessment· using such non-schemas.
5.2 Assessing Schema-ValidityWith a schema which satisfies the conditions expressed inErrors in Schema Construction and Structure (§5.1) above, the schema-validity of an element information item can be assessed. Three primary approaches to this are possible:
1 The user or application identifies a complex type definition from among the{type definitions} of the schema, and appeals toSchema-Validity Assessment (Element) (§3.3.4) (clause1.2);
2The user or application identifies a element declaration from among the{element declarations} of the schema, checks that its{name} and{target namespace} match the[local name] and[namespace name] of the item, and appeals toSchema-Validity Assessment (Element) (§3.3.4) (clause1.1);
3 The processor starts fromSchema-Validity Assessment (Element) (§3.3.4) with no stipulated declaration or definition, and either·strict· or·lax· assessment ensues, depending on whether or not the element information and the schema determine either an element declaration (by name) or a type definition (via xsi:type) or not.
The outcome of this effort, in any case, will be manifest in the [validation attempted] and [validity] properties on the element information item and its[attributes] and[children], recursively, as defined byAssessment Outcome (Element) (§3.3.5) andAssessment Outcome (Attribute) (§3.2.5). It is up to applications to decide what constitutes a successful outcome.
Note that every element and attribute information item participating in the·assessment· will also have a [validation context] property which refers back to the element information item at which·assessment· began. This item, that is the element information item at which·assessment· began, is called the validation root.
NOTE: This specification does not reconstruct the XML 1.0 notion of root in either schemas or instances. Equivalent functionality is provided for at·assessment· invocation, via clause2 above. NOTE: This specification has nothing normative to say about multiple·assessment· episodes. It should however be clear from the above that if a processor restarts·assessment· with respect to a post-schema-validation infoset some post-schema-validation infoset contributions from the previous·assessment· may be overwritten. Restarting nonetheless may be useful, particularly at a node whose [validation attempted] property is none, in which case there are three obvious cases in which additional useful information may result:·assessment· was not attempted because of a·validation· failure, but declarations and/or definitions are available for at least some of the[children] or[attributes];·assessment· was not attempted because a named definition or declaration was missing, but after further effort the processor has retrieved it.·assessment· was not attempted because it was skipped, but the processor has at least some declarations and/or definitions available for at least some of the[children] or[attributes].
5.3 Missing Sub-componentsAt the beginning ofSchema Component Details (§3), attention is drawn to the fact that most kinds of schema components have properties which are described therein as having other components, or sets of other components, as values, but that when components are constructed on the basis of their correspondence with element information items in schema documents, such properties usually correspond toQNames, and the·resolution· of suchQNames may fail, resulting in one or more values of or containing·absent· where a component is mandated.
If at any time during·assessment·, an element or attribute information item is being·validated· with respect to a component of any kind any of whose properties has or contains such an·absent· value, the·validation· is modified, as following:
In the case of attribute information items, the effect is as if clause1 ofAttribute Locally Valid (§3.2.4) had failed; In the case of element information items, the effect is as if clause1 ofElement Locally Valid (Element) (§3.3.4) had failed; In the case of element information items, processors may choose to continue·assessment·: see·lax assessment·.
Because of the value specification for[validation attempted] inAssessment Outcome (Element) (§3.3.5), if this situation ever arises, the document as a whole cannot show a[validation attempted] of full.
5.4 Responsibilities of Schema-aware ProcessorsSchema-aware processors are responsible for processing XML documents, schemas and schema documents, as appropriate given the level of conformance (as defined inConformance (§2.4)) they support, consistently with the conditions set out above.
A Schema for Schemas (normative)
The XML Schema definition for XML Schema: Structures itself is presented here as normative part of the specification, and as an illustrative example of the XML Schema in defining itself with the very constructs that it defines. The names of XML Schema language types, elements, attributes and groups defined here are evocative of their purpose, but are occasionally verbose.
There is some annotation in comments, but a fuller annotation will require the use of embedded documentation facilities or a hyperlinked external annotation for which tools are not yet readily available.
Since an XML Schema: Structures is an XML document, it has optional XML and doctype declarations that are provided here for completeness. The root schema element defines a new schema. Since this is a schema for XML Schema: Structures, the targetNamespace references the XML Schema namespace itself.
]>
B References (normative)
Extensible Markup Language (XML) 1.0, Second Edition, Tim Bray et al., eds., W3C, 6 October 2000. Seehttp://www.w3.org/TR/2000/REC-xml-20001006XML Information Set, John Cowan and Richard Tobin, eds., W3C, 16 March 2001. Seehttp://www.w3.org/TR/2001/WD-xml-infoset-20010316/Namespaces in XML, Tim Bray et al., eds., W3C, 14 January 1999. Seehttp://www.w3.org/TR/1999/REC-xml-names-19990114/XML Schema Requirements , Ashok Malhotra and Murray Maloney, eds., W3C, 15 February 1999. Seehttp://www.w3.org/TR/1999/NOTE-xml-schema-req-19990215XML Schema Part 2: Datatypes, Paul V. Biron and Ashok Malhotra, eds., W3C, 2 May 2001. Seehttp://www.w3.org/TR/2001/REC-xmlschema-2-20010502/datatypes.htmlXML Path Language, James Clark and Steve DeRose, eds., W3C, 16 November 1999. Seehttp://www.w3.org/TR/1999/REC-xpath-19991116XML Pointer Language (XPointer), Eve Maler and Steve DeRose, eds., W3C, 8 January 2001. Seehttp://www.w3.org/TR/2001/WD-xptr-20010108/
C Outcome Tabulations (normative)
To facilitate consistent reporting of schema errors and·validation· failures, this section tabulates and provides unique names for all the constraints listed in this document. Wherever such constraints have numbered parts, reports should use the name given below plus the part number, separated by a period (‘.‘). Thus for example cos-ct-extends.1.2 should be used to report a violation of the clause1.2 ofDerivation Valid (Extension) (§3.4.6).
C.1 Validation Rulescvc-assess-attrSchema-Validity Assessment (Attribute)cvc-assess-eltSchema-Validity Assessment (Element)cvc-attributeAttribute Locally Validcvc-auAttribute Locally Valid (Use)cvc-complex-typeElement Locally Valid (Complex Type)cvc-datatype-validDatatype Validcvc-eltElement Locally Valid (Element)cvc-enumeration-validenumeration validcvc-facet-validFacet Validcvc-fractionDigits-validfractionDigits Validcvc-idValidation Root Valid (ID/IDREF)cvc-identity-constraintIdentity-constraint Satisfiedcvc-length-validLength Validcvc-maxExclusive-validmaxExclusive Validcvc-maxInclusive-validmaxInclusive Validcvc-maxLength-validmaxLength Validcvc-minExclusive-validminExclusive Validcvc-minInclusive-validminInclusive Validcvc-minLength-validminLength Validcvc-model-groupElement Sequence Validcvc-particleElement Sequence Locally Valid (Particle)cvc-pattern-validpattern validcvc-resolve-instanceQName resolution (Instance)cvc-simple-typeString Validcvc-totalDigits-validtotalDigits Validcvc-typeElement Locally Valid (Type)cvc-wildcardItem Valid (Wildcard)cvc-wildcard-namespaceWildcard allows Namespace Name
C.2 Contributions to the post-schema-validation infosetattribute information item properties[attribute declaration] (Attribute Declaration)
[member type definition] (Attribute Validated by Type)
[member type definition anonymous] (Attribute Validated by Type)
[member type definition name] (Attribute Validated by Type)
[member type definition namespace] (Attribute Validated by Type)
[schema default] (Attribute Validated by Type)
[schema error code] (Validation Failure (Attribute))
[schema normalized value] (Attribute Validated by Type)
[schema specified] (Assessment Outcome (Attribute))
[type definition] (Attribute Validated by Type)
[type definition anonymous] (Attribute Validated by Type)
[type definition name] (Attribute Validated by Type)
[type definition namespace] (Attribute Validated by Type)
[type definition type] (Attribute Validated by Type)
[validation attempted] (Assessment Outcome (Attribute))
[validation context] (Assessment Outcome (Attribute))
[validity] (Assessment Outcome (Attribute))
element information item properties[element declaration] (Element Declaration)
[ID/IDREF table] (ID/IDREF Table)
[identity-constraint table] (Identity-constraint Table)
[member type definition] (Element Validated by Type)
[member type definition anonymous] (Element Validated by Type)
[member type definition name] (Element Validated by Type)
[member type definition namespace] (Element Validated by Type)
[nil] (Element Declaration)
[notation] (Validated with Notation)
[notation public] (Validated with Notation)
[notation system] (Validated with Notation)
[schema default] (Element Validated by Type)
[schema error code] (Validation Failure (Element))
[schema information] (Schema Information)
[schema normalized value] (Element Validated by Type)
[schema specified] (Element Default Value)
[type definition] (Element Validated by Type)
[type definition anonymous] (Element Validated by Type)
[type definition name] (Element Validated by Type)
[type definition namespace] (Element Validated by Type)
[type definition type] (Element Validated by Type)
[validation attempted] (Assessment Outcome (Element))
[validation context] (Assessment Outcome (Element))
[validity] (Assessment Outcome (Element))
ID/IDREF binding information item properties[binding] (ID/IDREF Table)
[id] (ID/IDREF Table)
Identity-constraint Binding information item properties[definition] (Identity-constraint Table)
[node table] (Identity-constraint Table)
namespace schema information information item properties[schema components] (Schema Information)
[schema documents] (Schema Information)
[schema namespace] (Schema Information)
schema document information item properties[document location] (Schema Information)
[document] (Schema Information)
C.3 Schema Representation Constraintsschema_referenceSchema Document Location Strategysrc-annotationAnnotation Definition Representation OKsrc-attributeAttribute Declaration Representation OKsrc-attribute_groupAttribute Group Definition Representation OKsrc-ctComplex Type Definition Representation OKsrc-elementElement Declaration Representation OKsrc-expredefIndividual Component Redefinitionsrc-identity-constraintIdentity-constraint Definition Representation OKsrc-importImport Constraints and Semanticssrc-includeInclusion Constraints and Semanticssrc-list-itemType-or-simpleTypeitemType attribute or simpleType childsrc-model_groupModel Group Representation OKsrc-model_group_defnModel Group Definition Representation OKsrc-multiple-enumerationsMultiple enumerationssrc-multiple-patternsMultiple patternssrc-notationNotation Definition Representation OKsrc-qnameQName Interpretationsrc-redefineRedefinition Constraints and Semanticssrc-resolveQName resolution (Schema Document)src-restriction-base-or-simpleTypebase attribute or simpleType childsrc-simple-typeSimple Type Definition Representation OKsrc-single-facet-valueSingle Facet Valuesrc-union-memberTypes-or-simpleTypesmemberTypes attribute or simpleType childrensrc-wildcardWildcard Representation OKst-restrict-facetsSimple Type Restriction (Facets)
C.4 Schema Component Constraintsag-props-correctAttribute Group Definition Properties Correctan-props-correctAnnotation Correcta-props-correctAttribute Declaration Properties Correctau-props-correctAttribute Use Correctc-fields-xpathsFields Value OKcos-all-limitedAll Group Limitedcos-applicable-facetsapplicable facetscos-aw-intersectAttribute Wildcard Intersectioncos-aw-unionAttribute Wildcard Unioncos-choice-rangeEffective Total Range (choice)cos-ct-derived-okType Derivation OK (Complex)cos-ct-extendsDerivation Valid (Extension)cos-element-consistentElement Declarations Consistentcos-equiv-classSubstitution Groupcos-equiv-derived-ok-recSubstitution Group OK (Transitive)cos-group-emptiableParticle Emptiablecos-list-of-atomiclist of atomiccos-no-circular-unionsno circular unionscos-nonambigUnique Particle Attributioncos-ns-subsetWildcard Subsetcos-particle-extendParticle Valid (Extension)cos-particle-restrictParticle Valid (Restriction)cos-seq-rangeEffective Total Range (all and sequence)cos-st-derived-okType Derivation OK (Simple)cos-st-restrictsDerivation Valid (Restriction, Simple)cos-valid-defaultElement Default Valid (Immediate)c-props-correctIdentity-constraint Definition Properties Correctc-selector-xpathSelector Value OKct-props-correctComplex Type Definition Properties Correctderivation-ok-restrictionDerivation Valid (Restriction, Complex)enumeration-required-notationenumeration facet value required for NOTATIONenumeration-valid-restrictionenumeration valid restrictione-props-correctElement Declaration Properties CorrectfractionDigits-totalDigitsfractionDigits less than or equal to totalDigitslength-minLength-maxLengthlength and minLength or maxLengthlength-valid-restrictionlength valid restrictionmaxExclusive-valid-restrictionmaxExclusive valid restrictionmaxInclusive-maxExclusivemaxInclusive and maxExclusivemaxInclusive-valid-restrictionmaxInclusive valid restrictionmaxLength-valid-restrictionmaxLength valid restrictionmgd-props-correctModel Group Definition Properties Correctmg-props-correctModel Group CorrectminExclusive-less-than-equal-to-maxExclusiveminExclusive <= maxExclusiveminExclusive-less-than-maxInclusiveminExclusive < maxInclusiveminExclusive-valid-restrictionminExclusive valid restrictionminInclusive-less-than-equal-to-maxInclusiveminInclusive <= maxInclusiveminInclusive-less-than-maxExclusiveminInclusive < maxExclusiveminInclusive-minExclusiveminInclusive and minExclusiveminInclusive-valid-restrictionminInclusive valid restrictionminLength-less-than-equal-to-maxLengthminLength <= maxLengthminLength-valid-restrictionminLength valid restrictionno-xmlnsxmlns Not Allowedno-xsixsi: Not Allowedn-props-correctNotation Declaration Correctp-props-correctParticle Correctrange-okOccurrence Range OKrcase-MapAndSumParticle Derivation OK (Sequence:Choice -- MapAndSum)rcase-NameAndTypeOKParticle Restriction OK (Elt:Elt -- NameAndTypeOK)rcase-NSCompatParticle Derivation OK (Elt:Any -- NSCompat)rcase-NSRecurseCheckCardinalityParticle Derivation OK (All/Choice/Sequence:Any -- NSRecurseCheckCardinality)rcase-NSSubsetParticle Derivation OK (Any:Any -- NSSubset)rcase-RecurseParticle Derivation OK (All:All,Sequence:Sequence -- Recurse)rcase-RecurseAsIfGroupParticle Derivation OK (Elt:All/Choice/Sequence -- RecurseAsIfGroup)rcase-RecurseLaxParticle Derivation OK (Choice:Choice -- RecurseLax)rcase-RecurseUnorderedParticle Derivation OK (Sequence:All -- RecurseUnordered)sch-props-correctSchema Properties Correctst-props-correctSimple Type Definition Properties CorrecttotalDigits-valid-restrictiontotalDigits valid restrictionwhiteSpace-valid-restrictionwhiteSpace valid restrictionw-props-correctWildcard Properties Correct
D Required Information Set Items and Properties (normative)
This specification requires as a precondition for·assessment· an information set as defined in[XML-Infoset] which supports at least the following information items and properties:
Attribute Information Item[local name],[namespace name],[normalized value]Character Information Item[character code]Element Information Item[local name],[namespace name],[children],[attributes],[in-scope namespaces] or[namespace attributes]Namespace Information Item[prefix],[namespace name]
This specification does not require any destructive alterations to the input information set: all the information set contributions specified herein are additive.
This appendix is intended to satisfy the requirements forConformance to the[XML-Infoset] specification.
E Schema Components Diagram (non-normative)
F Glossary (non-normative)
The listing below is for the benefit of readers of a printed version of this document: it collects together all the definitions which appear in the document above.
absentThroughout this specification, the term absent is used as a distinguished property value denoting absenceactual valueThe phrase actual value is used to refer to the member of the value space of the simple type definition associated with an attribute information item which corresponds to its·normalized value·assessmentthe word assessment is used to refer to the overall process of local validation, schema-validity assessment and infoset augmentationbase type definitionA type definition used as the basis for an·extension· or·restriction· is known as the base type definition of that definitioncomponent nameDeclarations and definitions may have and be identified by names, which are NCNames as defined by[XML-Namespaces]conformance to the XML Representation of Schemas·Minimally conforming· processors which accept schemas represented in the form of XML documents as described inLayer 2: Schema Documents, Namespaces and Composition (§4.2) are additionally said to provide conformance to the XML Representation of Schemas.content modelA particle can be used in a complex type definition to constrain the·validation· of the[children] of an element information item; such a particle is called a content modelcontext-determined declarationDuring·validation·, associations between element and attribute information items among the[children] and[attributes] on the one hand, and element and attribute declarations on the other, are established as a side-effect. Such declarations are called the context-determined declarationsdeclarationdeclaration components are associated by (qualified) name to information items being·validated·definitiondefinition components define internal schema components that can be used in other schema componentselement substitution groupThrough the new mechanism of element substitution groups, XML Schemas provides a more powerful model supporting substitution of one named element for anotherextensionA complex type definition which allows element or attribute content in addition to that allowed by another specified type definition is said to be an extensionfinalthe complex type is said to be final, because no further derivations are possiblefully conformingFully conforming processors are network-enabled processors which are not only both·minimally conforming· and·in conformance to the XML Representation of Schemas·, but which additionally must be capable of accessing schema documents from the World Wide Web according toRepresentation of Schemas on the World Wide Web (§2.7) andHow schema definitions are located on the Web (§4.3.2).implicitly containsA list of particles implicitly contains an element declaration if a member of the list contains that element declaration in its·substitution group·initial valuethe initial value of some attribute information item is the value of the[normalized value] property of that item. Similarly, the initial value of an element information item is the string composed of, in order, the[character code] of each character information item in the[children] of that element information itemitem isomorphic to a componentby an item isomorphic to a component is meant an information item whose type is equivalent to the component‘s, with one property per property of the component, with the same name, and value either the same atomic value, or an information item corresponding in the same way to its component value, recursively, as necessarylaxly assessedan element information item‘s schema validity may be laxly assessed if its·context-determined declaration· is not skip by·validating· with respect to the·ur-type definition· as perElement Locally Valid (Type) (§3.3.4)minimally conformingMinimally conforming processors must completely and correctly implement the·Schema Component Constraints·,·Validation Rules·, and·Schema Information Set Contributions· contained in this specificationNCNameAn NCName is a name with no colon, as defined in[XML-Namespaces]. When used in connection with the XML representation of schema components in this specification, this refers to the simple typeNCName as defined in[XML Schemas: Datatypes]normalized valueThe normalized value of an element or attribute information item is an·initial value· whose white space, if any, has been normalized according to the value of thewhiteSpace facet of the simple type definition used in its·validation·:partitionDefine a partition of a sequence as a sequence of sub-sequences, some or all of which may be empty, such that concatenating all the sub-sequences yields the original sequenceQNameA QName is a name with an optional namespace qualification, as defined in[XML-Namespaces]. When used in connection with the XML representation of schema components or references to them, this refers to the simple typeQName as defined in[XML Schemas: Datatypes]resolveWhenever the word resolve in any form is used in this chapter in connection with a·QName· in a schema document, the following definitionQName resolution (Schema Document) (§3.15.3) should be understoodrestrictionA type definition whose declarations or facets are in a one-to-one relation with those of another specified type definition, with each in turn restricting the possibilities of the one it corresponds to, is said to be a restrictionschema componentSchema component is the generic term for the building blocks that comprise the abstract data model of the schema.Schema Component ConstraintConstraints on the schema components themselves, i.e. conditions components must satisfy to be components at all. Located in the sixth sub-section of the per-component sections ofSchema Component Details (§3) and tabulated inSchema Component Constraints (§C.4)schema documentA document in this form (i.e. a
G DTD for Schemas (non-normative)
The DTD for XML Schema: Structures is given below. Note there is no implication here the schema must be the root element of a document.
Although this DTD is non-normative, any XML document which is not valid per this DTD, given redefinitions in its internal subset of the ‘p‘ and ‘s‘ parameter entities below appropriate to its namespace declaration of the XML Schema namespace, is almost certainly not a valid schema document, with the exception of documents with multiple namespace prefixes for the XML Schema namespace itself. Accordingly authoring XML Schema documents using this DTD and DTD-based authoring tools, and specifying it as the DOCTYPE of documents intended to be XML Schema documents and validating them with a validating XML parser, are sensible development strategies which users are encouraged to adopt until XML Schema-based authoring tools and validators are more widely available.
%xs-datatypes;
H Analysis of the Unique Particle Attribution Constraint (non-normative)
A specification of the import ofUnique Particle Attribution (§3.8.6) which does not appeal to a processing model is difficult. What follows is intended as guidance, without claiming to be complete.
Two non-group particles overlap if
They are both element declaration particles whose declarations have the same{name} and{target namespace}.
or
They are both element declaration particles one of which is in the other‘s·substitution group·.
or
They are both wildcards, and the intensional intersection of their{namespace constraint}s as defined inAttribute Wildcard Intersection (§3.10.6) is not the empty set.
or
One is a wildcard and the other an element declaration, and the{target namespace} of the element declaration, or of any member of its·substitution group·, is·valid· with respect to the{namespace constraint} of the wildcard.
A content model will violate the unique attribution constraint if it contains two particles which·overlap· and which either
are both in the{particles} of a choice or all group
or
may·validate· adjacent information items and the first has{min occurs} less than{max occurs}.
Two particles may·validate· adjacent information items if they are separated by at most epsilon transitions in the most obvious transcription of a content model into a finite-state automaton.
A precise formulation of this constraint can also be offered in terms of operations on finite-state automaton: transcribe the content model into an automaton in the usual way using epsilon transitions for optionality and unbounded maxOccurs, unfolding other numeric occurrence ranges and treating the heads of substitution groups as if they were choices over all elements in the group, but using not element QNames as transition labels, but rather pairs of element QNames and positions in the model. Determinize this automaton, treating wildcard transitions as opaque. Now replace all QName+position transition labels with the element QNames alone. If the result has any states with two or more identical-QName-labeled transitions from it, or a QName-labeled transition and a wildcard transition which subsumes it, or two wildcard transitions whose intentional intersection is non-empty, the model does not satisfy the Unique Attribution constraint.
I References (non-normative)
Document Content Description for XML (DCD), Tim Bray et al., eds., W3C, 10 August 1998. Seehttp://www.w3.org/TR/1998/NOTE-dcd-19980731Document Definition Markup Language, Ronald Bourret, John Cowan, Ingo Macherius, Simon St. Laurent, eds., W3C, 19 January 1999. Seehttp://www.w3.org/TR/1999/NOTE-ddml-19990119 Schema for Object-oriented XML, Andrew Davidson et al., eds., W3C, 1998. Seehttp://www.w3.org/1999/07/NOTE-SOX-19990730/Schema for Object-oriented XML, Version 2.0, Andrew Davidson, et al., W3C, 30 July 1999. Seehttp://www.w3.org/TR/NOTE-SOX/XML-Data Reduced, Charles Frankston and Henry S. Thompson, 3 July 1998. Seehttp://www.ltg.ed.ac.uk/~ht/XMLData-Reduced.htm XML-Data, Andrew Layman et al., W3C, 05 January 1998. Seehttp://www.w3.org/TR/1998/NOTE-XML-data-0105/XML Schema Part 0: Primer, David C. Fallside, ed., W3C, 2 May 2001. Seehttp://www.w3.org/TR/2001/REC-xmlschema-0-20010502/primer.html
J Acknowledgements (non-normative)
The following have contributed material to this draft:
David Fallside, IBM Scott Lawrence, Agranat Systems Andrew Layman, Microsoft Eve L. Maler, Sun Microsystems Asir S. Vedamuthu, webMethods, Inc
The editors acknowledge the members of the XML Schema Working Group, the members of other W3C Working Groups, and industry experts in other forums who have contributed directly or indirectly to the process or content of creating this document. The Working Group is particularly grateful to Lotus Development Corp. and IBM for providing teleconferencing facilities.
The current members of the XML Schema Working Group are:
Jim Barnette, Defense Information Systems Agency (DISA); Paul V. Biron, Health Level Seven; Don Box, DevelopMentor; Allen Brown, Microsoft; Lee Buck, TIBCO Extensibility; Charles E. Campbell, Informix; Wayne Carr, Intel; Peter Chen, Bootstrap Alliance and LSU; David Cleary, Progress Software; Dan Connolly, W3C (staff contact); Ugo Corda, Xerox; Roger L. Costello, MITRE; Haavard Danielson, Progress Software; Josef Dietl, Mozquito Technologies; David Ezell, Hewlett-Packard Company; Alexander Falk, Altova GmbH; David Fallside, IBM; Dan Fox, Defense Logistics Information Service (DLIS); Matthew Fuchs, Commerce One; Andrew Goodchild, Distributed Systems Technology Centre (DSTC Pty Ltd); Paul Grosso, Arbortext, Inc; Martin Gudgin, DevelopMentor; Dave Hollander, Contivo, Inc (co-chair); Mary Holstege, Invited Expert; Jane Hunter, Distributed Systems Technology Centre (DSTC Pty Ltd); Rick Jelliffe, Academia Sinica; Simon Johnston, Rational Software; Bob Lojek, Mozquito Technologies; Ashok Malhotra, Microsoft; Lisa Martin, IBM; Noah Mendelsohn, Lotus Development Corporation; Adrian Michel, Commerce One; Alex Milowski, Invited Expert; Don Mullen, TIBCO Extensibility; Dave Peterson, Graphic Communications Association; Jonathan Robie, Software AG; Eric Sedlar, Oracle Corp.; C. M. Sperberg-McQueen, W3C (co-chair); Bob Streich, Calico Commerce; William K. Stumbo, Xerox; Henry S. Thompson, University of Edinburgh; Mark Tucker, Health Level Seven; Asir S. Vedamuthu, webMethods, Inc; Priscilla Walmsley, XMLSolutions; Norm Walsh, Sun Microsystems; Aki Yoshida, SAP AG; Kongyi Zhou, Oracle Corp.
The XML Schema Working Group has benefited in its work from the participation and contributions of a number of people not currently members of the Working Group, including in particular those named below. Affiliations given are those current at the time of their work with the WG.
Paula Angerstein, Vignette Corporation; David Beech, Oracle Corp.; Gabe Beged-Dov, Rogue Wave Software; Greg Bumgardner, Rogue Wave Software; Dean Burson, Lotus Development Corporation; Mike Cokus, MITRE; Andrew Eisenberg, Progress Software; Rob Ellman, Calico Commerce; George Feinberg, Object Design; Charles Frankston, Microsoft; Ernesto Guerrieri, Inso; Michael Hyman, Microsoft; Renato Iannella, Distributed Systems Technology Centre (DSTC Pty Ltd); Dianne Kennedy, Graphic Communications Association; Janet Koenig, Sun Microsystems; Setrag Khoshafian, Technology Deployment International (TDI); Ara Kullukian, Technology Deployment International (TDI); Andrew Layman, Microsoft; Dmitry Lenkov, Hewlett-Packard Company; John McCarthy, Lawrence Berkeley National Laboratory; Murata Makoto, Xerox; Eve Maler, Sun Microsystems; Murray Maloney, Muzmo Communication, acting for Commerce One; Chris Olds, Wall Data; Frank Olken, Lawrence Berkeley National Laboratory; Shriram Revankar, Xerox; Mark Reinhold, Sun Microsystems; John C. Schneider, MITRE; Lew Shannon, NCR; William Shea, Merrill Lynch; Ralph Swick, W3C; Tony Stewart, Rivcom; Matt Timmermans, Microstar; Jim Trezzo, Oracle Corp.; Steph Tryphonas, Microstar
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