RDF is short for Resource Description Framework. RDF is the language for describing resources and contents in the semantic web. In the semantic web RDF is used to describe resources on the web. Resources are addressed by a unique URI. A URI looks like a normal Internet URL. Look at the following fragment of a RDF file: <?xml version="1.0"?> <rdf:RDF     xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"     xmlns:owl="http://www.w3.org/2002/07/owl#"     xmlns:xsd="http://www.w3.org/2001/XMLSchema#"     xmlns="http://example.org/pets#"     xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"   xml:base="http://example.org/pets">   <owl:Class rdf:ID="Goldfish"> [...]