RDF stands for Resource Description Framework and defines an XML-based standard used to describe resources on the Web. In all the important ways, the ultimate clearinghouse for RDF information is located on Dave Beckett's Web site (Planet RDF), where his Resource Guide provides as complete a collection of pointers to information about RDF, plus related standards, documents, publications and ever so much more.
Though RDF has been available for some time, it's neither terribly well-known nor widely understood. Although the most recent W3C recommendations are all dated February 10, 2004 (Dave Beckett is listed as the Editor for the RDF/XML Syntax Specification, along with Schema, Primer, Semantics and test cases documents), RDF is perhaps best known for its use with other XML applications, most notably Real Simple Syndication (aka RSS).
Like the OWL Web Ontology Language, however, RDF is a key ingredient in creating a Semantic Web, where meaning is represented and conveyed using metadata above and beyond the language used in the content itself. RDF is designed to provide a framework for such metadata, most especially to help facilitate how applications can use computer-based or machine-created information on the Web. In other words, RDF is designed to support automated processing (search, identification, categorization and qualification) of Web resources. This explains why RDF is important for many kinds of activities, including:
- access and use controls, in describing intellectual property (and reusability) rights associated with specific Web pages
- cataloging, in describing the content available in Web pages and the relationships among content items on Web sites, plus other kinds of digital information repositories (libraries, collections and so forth)
- content rating, in using metadata to apply rating schemes
- knowledge sharing and exchange, in enabling intelligent software agents to request particular types of knowledge from the client side and to respond to such requests from the server side
- search, in its ability to aid resource discovery and describe arbitrary collections of Web pages
RDF excels at providing a declarative syntax and semantics for representing metadata of all kinds. This language is declarative and uses standardized XML syntax to make statements about properties for items on the Web, as well as about relationships between or among such items on the Web. An item may be nearly anything that can take on a Web address: a Web page, a graphic, data files of many kinds or even other kinds of metadata (XML files, style sheets and so forth).
RSS comes into the picture when you understand that RDF exists to permit independent communities to create vocabularies to meet specific needs -- in the RSS case, vocabularies related to syndicated feeds of all kinds -- where the meanings of terms in such vocabularies must be spelled out in great detail. These vocabulary descriptions are known as RDF Schemas and they define the meanings for, characteristics associated with and the relationships between and among the set of properties for all items covered in the vocabulary. Such vocabularies are assigned Web addresses, in the same way that XML namespaces use URLs to identify themselves uniquely and unambiguously.
Thus, while many XML developers won't interact with RDF directly unless they find themselves developing a new vocabulary for their own use or extending an existing one for the same reason, many will benefit from its capabilities. That's why learning a little more about the Resource Description Framework is truly worthwhile.
About the author
Ed Tittel is a freelance writer and trainer whose background as a database developer and networking professional drew him inexorably into the Web and markup languages. The author of numerous books and articles on HTML and XML, Tittel has covered XML topics for TechTarget since 2000.