Web 2.0, a phrase coined by O'Reilly Media in 2004, refers to a perceived or proposed second generation of Internet-based services - such as social networking sites, communication tools that emphasize online collaboration and sharing among users.
Since 2004, some technicians and markets have adopted the phrase. However the exact meaning remains open to debate, notably Tim Berners Lee, have questioned whether the term has meaning.
Web 2.0 hints at improved form of WWW. Some advocates suggest weblogs, social bookmarks, RSS feeds, Web APIs, and online Web services imply a significant change in web usage.
At the early time of Web 2.0, which employed as a synonym for "Semantic Web", and indeed they are two concept and they complement each other.
Tim O'Reilly give out his "4+1" level in the hierarchy of Web 2.0 which is embodied by examples of companies or products:
• Level 3 application, the most "web 2.0", which could only exist on the internet, deriving their power from the human connections and network effects Web 2.0 makes possible, and growing in effectiveness the more use them. He gave as examples: eBay, Wikipedia, Skype.
• Level 2 application, which can operate offline but gain advantages from going online, such as Flickr, Webshot.
• Level 1 application, also available offline but gain feature online, e.g. Writely (since 10 Oct 2006: Google Docs & Spreadsheets, offering group-editing capability online) and iTunes.
• Level 0 applications, would work as well offline, such as Yahoo! Local, and Google Maps.
• None-web application, like email, IM tools, and telephone.
Web 2.0 websites exhibit some basic characteristics.
• Network as platform;
• Users owning the data on the site and exercising control over that data (YouTube, weblog);
• An architecture of participation and democracy that encourages users to add value to the application as they use it (Wikipedia, Flickr);
• A rich, interactive, user-friendly interface based on Ajax or similar; frameworks (Google map);
• Some social-networking aspects;
• Public goods.
A web 2.0 website features a number of the following techniques:
• Ajax-based (rich application techniques)
• CSS
• Semantically valid XHTML / the use of Microformats
• Syndication and aggregation of data in RSS/Atom
• Clean and meaningful URLs
• Extensive use of folksonomies
• Weblog publishing
• Mashups
• REST or XML Webservices APIs
Web 2.0 infrastructure may need the following major protocols:
• REST (Representational State Transfer) indicates a way to access and manipulate data on a server using the HTTP verbs GET, POST, PUT and Delete.
• SOAP involves POSTing XML messages and requests a server that may contain quite complex, but pre-defined, instructions for the server to follow.
(in both protocol, API defines access to the service. Servers use proprietary APIs, but standard web-service APIs have also come into wide use. Most communications with web services involve some form of XML.
Criticism issues involve in the Web 2.0:
• What "Web 2.0" actually means, implies, or requires, the term mean different things to different people. (Some company proclaims itself "Web 2.0" for attempting at self-promotion than actual endorsement of the ideas behind Web 2.0. Some people still insist on the idea of Web 2.0, which doesn't mean the new version of WWW, but just continues to use "Web 1.0" technologies and concepts.)
• May cause "a second bubble" or "Bubble 2.0". Too many companies attempt to build up product with lack of business model.
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