The Resource Description Framework (RDF) is a language for representing information about resources in the World Wide Web and has become a quite popular Semantic Web representation formalism. It is particularly intended for representing metadata about Web resources, such as the title and author of a Web page. RDF is based on the idea of identifying things using identifiers and describing resources in terms of simple properties and property values. RDF properties may be thought of as attributes of resources and in this sense correspond to traditional attribute-value pairs. The system is arranged in groups of rules that capture the semantic conditions of models.