An integrated system for knowledge representation, consisting of a structural component and a relational component, is discussed, and its application to Semantic Web is outlined. Grounded upon Description Logics (DL), the structural component enables representation of ontologies along with RDF annotations of Web contents, and various kinds of ontology-based reasoning. The relational component, by contrast, allows one to describe relationships between individuals using an extended form of Horn rules, in which terminological membership constraints can be specified. Reasoning process in the...