The Definition of Web 2.0

Definition

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Web 2.0 encapsulates the idea of the proliferation of interconnectivity and interactivity of web-delivered content. Tim O'Reilly regards Web 2.0 as the way that business embraces the strengths of the web and uses it as a platform. O'Reilly considers that Eric Schmidt's abridged slogan, don't fight the Internet, encompasses the essence of Web 2.0 — building applications and services around the unique features of the Internet, as opposed to expecting the Internet to suit as a platform (effectively "fighting the Internet").
In the opening talk of the first Web 2.0 conference, O'Reilly and John Battelle summarized what they saw as the themes of Web 2.0. They argued that the web had become a platform, with software above the level of a single device, leveraging the power of "The Long Tail," and with data as a driving force. According to O'Reilly and Battelle, an architecture of participation where users can contribute website content creates network effects. Web 2.0 technologies tend to foster innovation in the assembly of systems and sites composed by pulling together features from distributed, independent developers. (This could be seen as a kind of "open source" or possible "Agile" development process, consistent with an end to the traditional software adoption cycle, typified by the so-called "perpetual beta").

Web 2.0 technology encourages lightweight business models enabled by syndication of content and of service and by ease of picking-up by early adopters.

O'Reilly provided examples of companies or products that embody these principles in his description of his four levels in the hierarchy of Web 2.0 sites:

Level-3 applications, the most "Web 2.0"-oriented, exist only on the Internet, deriving their effectiveness from the inter-human connections and from the network effects that Web 2.0 makes possible, and growing in effectiveness in proportion as people make more use of them. O'Reilly gave eBay, Craigslist, Wikipedia, del.icio.us, Skype, dodgeball, and AdSense as examples.
Level-2 applications can operate offline but gain advantages from going online. O'Reilly cited Flickr, which benefits from its shared photo-database and from its community-generated tag database.
Level-1 applications operate offline but gain features online. O'Reilly pointed to Writely (now Google Docs & Spreadsheets) and iTunes (because of its music-store portion).
Level-0 applications work as well offline as online. O'Reilly gave the examples of MapQuest, Yahoo! Local, and Google Maps (mapping-applications using contributions from users to advantage could rank as "level 2", like Google Earth). In addition, Gmail.