Approximation of Ontologies in Casl

Abstract. In this paper we present methods to generate a Description Logic (DL) theory from a given First Order Logic (FOL) theory, such that each DL axiom is entailed by the given FOL theory. This is ob-tained by rewriting the given FOL formulas. If this method is applied to an ontology specification in FOL the resulting DL specification is still grounded on the same semantics but clearly weaker than the FOL specifi-cation. The benefit of specification in DL is that it is decidable, and that efficient reasoning procedures are also available as implemented in tools such as Racer, Fact++ or Pellet. Such ontologies in DL could be used for knowledge representation systems and the semantic web where efficient and decidable reasoning plays a major role. These weakening strategies are described with Casl (Common Algebraic Specification Language), and one of its sublogics Casl-DL, and will be integrated into Hets (Het-erogeneous Tool Set).