D.: A defeasible ontology language

Abstract. We extend the description logic ¢¤£¦¥¦§©¨��� � with a preference order on the axioms. With this strict partial order certain axioms can be overruled, if defeated with more preferred ones. Furthermore, we impose a preferred model semantics, thus effectively introducing nonmonotonicity into ¢�£¦¥�§�¨��� �. Since a description logic can be viewed as an ontology language, or a proper translation of one, we obtain a defeasible ontology language. Finally, we argue that such a defeasible language may be usefully applied for learning and integrating ontologies.