The Semantic Web is the brain child of Tim Berners-Lee, the father of the World Wide Web. The World Wide Web is a vast network of human-understandable data made possible by the inter-operable information format of HTML. The Semantic Web is an extension of this, both in idea and in implementation, to make a vast network of data that is understandable both by humans and machines.
It is evident from the large numbers of APIs available that allow developers access to particular Web sites that people want to treat the Web as data. Different APIs from different Web sites are unlikely to follow the same format, however, even if they do allow access to similar data. If you want to build software that can interpret the results of these API calls, you have to write a separate interface to each API, and if a new site comes along, you have to write a new interface. With the Semantic Web, that problem is removed and data is available in standard formats directly from the Web site, rather than having to access it with an API. You write one interface to the Semantic Web standards, and your software interfaces with all Web sites that implement these same standards.
The key Semantic Web technologies in this tutorial are RDF, RDFa, microformats and GRDDL.
Resource Description Framework (RDF) is the base standard of Semantic Web technologies. It allows the representation of knowledge in an unambiguous format, which can then be represented in XML (“serialized to XML” as it is called) that allows computers to reason about that knowledge. To make your Web site part of the Semantic Web, it must be possible to extract RDF from it.
Microformats are not so much standards as design patterns. By using standard HTML and XHTML in a formalized way, extra semantic value can be inferred from that markup. Microformats represent commonly occurring features of Web pages such as people (hCard), events (hCalendar), weblogs (hAtom), curriculum vitae (hResume), and reviews (hReview). You can derive RDF from microformats with GRDDL.
RDFa is technique to embed RDF into XHTML markup. To do this, you extend XHTML elements with some extra attributes which then map the constructs of RDF directly into the markup of the page. You can derive RDF directly from RDFa documents, or extract it using GRDDL.
Gleaning Resource Descriptions from Dialects of Languages (GRDDL—pronounced ‘griddle’), allows you to derive RDF from documents that are not themselves RDF. Microformats, with their regularized use of HTML, are ideal targets for this as is RDFa, but it is possible to write a transformation for any Web page (or set of similar Web pages) to generate some appropriate RDF. The idea of GRDDL is to bootstrap the Semantic Web to quickly get to a critical mass of Semantic Web content.
Click here for example social networking app using the technology discussed above.
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Tags: GRDDL, microformats, RDF, RDFa, semantic, web standards