Abstract

Knowledge representation and reasoning on the Semantic Web is done by means of ontologies. While the quest for suit-able ontology languages is still ongoing, OWL [5] has been established as a core standard. It comes in three flavours, as OWL Full, OWL DL and OWL Lite, where OWL Full con-tains OWL DL, which in turn contains OWL Lite. The lat-ter two coincide semantically with certain description logics and can thus be considered fragments of first-order predicate logic. OWL ontologies can be understood to consist of two parts, one intensional, the other extensional. In description log-ics terminology, the intensional part consists of a TBox and an RBox, and contains knowledge about concepts (called classes) and complex relations between them (called roles). The extensional part consists of an ABox, and contains