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Resource Description Framework (RDF)

Support XML applications with formal metadata

developerWorks

Level: Intermediate

Contributors: W3C

06 Feb 2007
Updated 25 Apr 2007

Resource Description Framework (RDF) is a model for describing collections of formalized statements about a Web resource. You can also think of RDF as a metadata system for the Web. Learn about this standard and about its relationship with the Semantic Web, Web Ontology Language (OWL), and more.

For almost as long as the World Wide Web Consortium (W3C) has worked toward next-generation markup technology in the form of XML, it has also worked toward next-generation technology for formal description of Web resources. Resource Description Framework (RDF) [W3C Recommendation] is a model for describing collections of statements about a Web resource. These statements are conceptualized as triples, each of which has a subject, which is a Uniform Resource Identifier (URI); a predicate, which is also a URI; and an object, which is a URI or literal data value. To get the flavor of such statements, think of an HTML meta tag that gives the description of a Web page. If recast as RDF, the subject would be the URI of the Web page itself, the predicate would be a standard URI signifying a general description, and the object would be the actual text of the description. By making heavy use of URIs, RDF seeks to minimize ambiguity about the identity of components of these statements and thus make them formal enough for machine processing. Whether RDF succeeds in this goal is up for debate, but RDF is well-known for its active community and broad range of tools.

RDF is the backbone of the W3C's Semantic Web activity; the Semantic Web is a vision of a Web not just of presentation of content, but also of annotation of content to help frame its meaning. For example, in a Semantic Web, one can make a distinction between the concept of "python," a kind of snake, and "python," a computer programming language, while describing Web resources. RDF is standardized in a large stack of specifications, including the following:

OWL

Web Ontology Language (OWL) [W3C Recommendation] is an application of RDF, often encoded in RDF/XML, that adds a rich vocabulary that you can use to formally classify and reason about RDF resources. SPARQL Query Language for RDF [in development] is a special syntax for querying RDF data, and Gleaning Resource Descriptions from Dialects of Languages (GRDDL) [in development] is a system for extracting RDF data from XML documents. GRDDL has recently come into some prominence with the popularity of microformats on the Web. Another RDF-related specification that fits into the microformats puzzle is RDFa Syntax [in development], which is a special set of attributes for embedding RDF data within XML formats such as XHTML.


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