The hierarchical structure of DDC and RDF suggest a mutual understanding. So if you have not used library services. Either at a library or online and really wish to understand RDF, go to a library today. After reading what you find below.
The Dewey Decimal Classification (DDC) system is the world's most widely used library classification system. The system was conceived by Melvil Dewey in 1873 and first published in 1876. As a youngster you probably used the card system. Today most libraries use an electronic version.
The Resource Description Framework (RDF) provides a domain-neutral foundation on which extensible element sets can be defined and expressed in a standard notation. An RDF data model and an RDF schema are defined representing the element set and the classifier is configured to output the elements in RDF syntax according to the defined schema.
The World Wide Web Consortium has recently published a preliminary draft specification for the Resource Description Framework (RDF). RDF is intended to provide a common framework for the exchange of machine-understandable information on the Web. The specification provides an abstract model for representing arbitrarily complex statements about networked resources, as well as a concrete XML-based syntax for representing these statements in textual form. RDF relies heavily on the notion of standard vocabularies, and work is in progress on a 'schema' mechanism that will allow user communities to express their own vocabularies and classification schemes within the RDF model.
When communities or services make an RDF description of their collections available, it would be possible to build hierarchical 'views' of the distributed services offering a user interface organized by subject-classification rather than by physical location of the resource.