Chapter 3 - RDF
While XML is a universal language for defining markup, it does not provide with any means of talking
about the semantics (meaning) of data. For example, there is no intended meaning associated with the
nesting of tags; it is up to each application to interpret the nesting.
RDF is a language for describing resources. Its basic building block is a statement, a triple consisting
of an entity (called resource in Web terminology), a property, and a value (which may be another resource).
Essentially, a statement is a fact P(a,b) where P is a binary property, and a,b are resources. In the
Semantic Web design, RDF defines a layer residing on top of XML. As a consequence, RDF has been given a
syntax in XML.
RDF is domain-independent in that no it makes no assumption about a particular domain of use. It is up
to the user to define her own terminology in a schema language called RDF Schema. In essence, RDF Schema is
a primitive ontology language offering the following features:
Organisation of objects in classes (professor, staff member, student, course, undergraduate course) and
binary properties (teaches, studies, works in).
Subclass (all professors are staff members) and subproperties (everyone who heads a department is member
of that department) relationships.
Domain (only academic staff can teach courses) and range (one can teach courses only) restrictions on
RDF and RDF Schema provide the basic core languages for the Semantic Web.