Rdf Primer / quote 46 of 55
Vocabularies for types, properties and values
However, in addition to the basic techniques for describing things using RDF statements discussed so far, it should be clear that people or organizations also need a way to describe the vocabularies (terms) they intend to use in those statements, specifically, vocabularies for: - describing types of things (like exterms:Person) - describing properties (like exterms:age and exterms:creation-date), and - describing the types of things that can serve as the subjects or objects of statements involving those properties (such as specifying that the value of an exterms:age property should always be an xsd:integer).
The basis for describing such vocabularies in RDF is the RDF Vocabulary Description Language 1.0: RDF Schema [RDF-VOCABULARY],