什么是Web 2.0

Web 2.0
From Wikipedia, the free encyclopedia.
Web 2.0 is a term often applied to a perceived ongoing transition of the World Wide Web from a collection of websites to a full-fledged computing platform serving web applications to end users. The proponents of this thinking expect that ultimately Web 2.0 services will replace desktop computing applications for many purposes.

Contents
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1 Overview
1.1 Origin of the term
1.2 Comparison with Semantic Web
2 Technology
2.1 Content syndication
2.2 Web services
2.3 Server software
3 Social impact
4 Business impact
5 External links
5.1 Examples

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Overview
The original conception of the web (in this context, labelled Web 1.0) comprised static HTML pages that were updated rarely, if at all. The success of the dot-com era depended on a more dynamic web (sometimes labeled Web 1.5) where content management systems served dynamic HTML web pages created on the fly from an ever-changing content database. In both senses, so-called eyeballing was considered intrinsic to the web experience, thus making page hits and visual aesthetics important factors.

Proponents of the Web 2.0 approach believe that web usage is increasingly oriented toward interaction and rudimentary social networks, which can serve content that exploits network effects with or without creating a visual, interactive web page. In one view, Web 2.0 sites act more as points of presence, or user-dependent web portals, than as traditional websites.

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Origin of the term
The term was coined by Dale Dougherty of O'Reilly Media brainstorming with Craig Cline of MediaLive to develop ideas for a conference that they could jointly host. Dougherty suggested that the web was in a renaissance, with changing rules and evolving business models. Dougherty gave examples — "DoubleClick was Web 1.0; Google AdSense is Web 2.0. Ofoto is Web 1.0; Flickr is Web 2.0." — rather than definitions, and recruited John Battelle for a business perspective, and O'Reilly Media, Battelle, and MediaLive launched the first Web 2.0 Conference in October 2004. The second annual conference will be held in October 2005.

In their conference opening talk, O'Reilly and Battelle summarized key principles they believe characterize web 2.0 applications: The web as platform; data as the "Intel Inside"; network effects driven by an "architecture of participation"; innovation in assembly of systems and sites composed by pulling together features from distributed, independent developers; lightweight business models enabled by content and service syndication; the end of the software adoption cycle ("the perpetual beta"); software above the level of a single device; leveraging the power of "the Long Tail."

The use of a software-style version number is a way of implying that the web as a whole is being rewritten and re-released as a new product with significant enhancements.

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Comparison with Semantic Web
An earlier usage of the phrase Web 2.0 was a synonym for Semantic Web. The two concepts are similar and complementary. The combination of social networking systems such as FOAF and XFN with the development of tag-based folksonomies and delivered through blogs and wikis creates a natural basis for a semantic environment.

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Technology
The technology infrastructure of Web 2.0 is complex and evolving, but includes server software, content syndication, messaging protocols, standards-based browsers, and various client applications. (Non-standard browser plug-ins and enhancements are generally eschewed.) These differing but complementary approaches provide Web 2.0 with information storage, creation, and dissemination capabilities that go beyond what was formerly expected of websites.

A website could be said to be built using Web 2.0 technologies if it featured a number of the following techniques:

Technical:

CSS, semantically valid XHTML markup, and Microformats
Unobtrusive Rich Application techniques (such as Ajax)
Syndication of data in RSS/ATOM
Aggregation of RSS/ATOM data
Clean and meaningful URLs
Support posting to a weblog
RESTian (preferred) or XML Webservice APIs
Some social networking aspects (share your data with friends, etc)
General:

The site should not act as a "walled garden" - it should be easy to get data in and out of the system.
Users should own their own data on the site
Purely web based - most successful web 2.0 sites can be used almost entirely through the browser
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Content syndication
The first and most important evolution towards Web 2.0 involves the syndication of website content, using standardized protocols which permit end-users to make use of a site's data in another context, ranging from another website, to a browser plug-in, or a separate desktop application. Protocols which permit syndication include RSS, RDF (as in RSS 1.1), and Atom, all of which are flavors of XML. Specialized protocols such as FOAF and XFN (both for social networking) extend functionality of sites or permit end-users to interact without centralized websites. See microformats for more specialized data formats.

Due to the recent development of these trends, many of these protocols are de facto rather than formal standards.

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Web services
Two-way messaging protocols are one of the key elements of the Web 2.0 infrastructure. The two major types are the RESTful and SOAP methods. REST (Representational State Transfer) indicates a type of web service invocation where the client transfers the state of all transactions. SOAP (Simple Object Access Protocol) and similar lightweight methods depend on the server to retain state information. In both cases, the service is invoked through an Application Program Interface (API). Often this API is customized to the website's specific needs, but standard web services APIs (for example, posting to a blog) are also widely used. Generally the common language of web services is XML (Extensible Markup Language), but this is not guaranteed, and proprietary variations abound.

Recently, a hybrid form known as Ajax has evolved to improve the user experience in browser-based web applications. This may be used in proprietary forms (as in Google Maps) or in open form utilizing a web services API, a syndication feed, or even screen scraping.

Broadly speaking, syndication is a type of web service, but this usage is becoming less common.

See also WSDL (Web Services Description Language) and List of Web service specifications (aka WS-*).

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Server software
Web 2.0 functionality builds on the existing web server architecture, but puts much greater emphasis on back-end software. Syndication differs only nominally from dynamic content management publishing methods, but web services typically require much more robust database and workflow support, and become very similar to the traditional intranet functionality of an application server. Vendor approaches to date fall under either a universal server approach, which bundles most of the necessary functionality in a single server platform, or a web server plug-in approach, which uses standard publishing tools enhanced with API interfaces and other tools. Regardless of the approach chosen, the evolutionary path toward Web 2.0 is not expected to be significantly altered by these choices.

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Social impact
The syndication and messaging capabilities found in Web 2.0 suggest the potential to create a more tightly-woven social fabric among disparate online communities. While terms have been invented to treat these communities collectively, including blogosphere for the world of weblogs, syndisphere for content syndication feeds, and wikisphere for wikis, other observers consider the wording and the implied value to be excessive.

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Business impact
The potential for exponential business growth as a result of the effects of Web 2.0 comes down to the difference between human-instigated value consumption and computer-instigated value consumption.

It is entirely possible for identification and consumption of value to occur without human intervention as a result of Web 2.0. Organizations will increasingly syndicate their value propositions using syndication formats such as RSS/Atom/RDF. In addition to value syndication. Web Service endpoint publishing will simplify the process of consuming the syndicated value.

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External links
Web 2.0 Conference
Relax, Everything Is Deeply Intertwingled: Web 2.0
Design for Web 2.0
Web 2.0 Definition and Tagging
Jeremy Zawodny's blog: Web2 Archives
Kingsley Idehen's blog: Web2 articles
Vancouver Web 2.0 Forum (Van2)
The Businessperson's Guide to the Web: Past, Present & Future
A Cumulative Web 2.0 definition
Tim Bray's comments on Web 2.0
Tim O'Reilly's response to Tim Bray
Web 2.0 Forum
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Examples
These companies, recognized as major "Web 1.0" successes, offer some combination of syndicated content and web services:

Amazon.com Web Services
Google Web APIs
Yahoo! Search Web Services
These companies are widely thought of as Web 2.0 examples:

Flickr
del.icio.us, the shared bookmarking service that popularized Tagging
Google Maps, and more specifically, sites like housingmaps.com that are enabled by Google Maps