This Chapter is a presentation of Resource Description Framework (RDF) recommended by World Wide Web Consortium (W3C), to model meta-data about the resources of a web. It is described in both the documents [1] and [2]; the former focuses mainly on syntactical aspects while latter addresses the definition of a vocabularies (often called schemas). Though this is the pragmatic approach, We will use slightly different plan, more suited to our own goals (using RDF in the knowledge representation systems). The first section will describe a RDF model, which is the fundamental syntax. Second section will present the semantic aspects of RDF, the concepts and the corresponding vocabulary. The last section describes the XML syntax proposed in [1].

We can distinguish three kinds of concepts in the RDF: The fundamental concepts, The schema-definition concepts (useful for defining a new vocabularies) and The utility concepts (are the concepts which are not absolutely necessary, but are likely to be useful in any of the application domain).

An RDF document is the list of descriptions. Usually each description applies to one resource, and contains the list of properties. Property values are either the URIs, literals or any other Descriptions.

In XML, the RDF meta-data are embedded in the element named "rdf:RDF". This element do contains the sequence of elements named RDF:Description. Those elements can have one of the two attributes either RDF:about or the RDf:ID (but not both of them).