A Preferential Tableaux Calculus for

Abstract. Nonmonotonic extensions of description logics (DLs) allow for default and local closed-world reasoning and are an acknowledged desired feature for applications, e.g. in the Semantic Web. A recent ap-proach to such an extension is based on McCarthy’s circumscription, which rests on the principle of minimising the extension of selected pred-icates to close off dedicated parts of a domain model. While decidabil-ity and complexity results have been established in the literature, no practical algorithmisation for circumscriptive DLs has been proposed so far. In this paper, we present a tableaux calculus that can be used as a decision procedure for concept satisfiability with respect to concept-circumscribed ALCO knowledge bases. The calculus builds on existing tableaux for classical DLs, extended by the notion of a preference clash to detect the non-minimality of constructed models.