An algorithm to compute circumscription

摘要

McCarthy's theory of circumscription appears to be the most powerful among various formalizations of nonmonotonic reasoning designed to handle incomplete and negative information in knowledge representation systems. In this paper we describe a query answering algorithm for circumscriptive theories.The Closed-World Assumption (CWA) and its generalizations, the Generalized Closed-World Assumption (GCWA) and the Extended Closed-World Assumption (ECWA), can be considered as special forms of circumscription. Consequently, our algorithm also applies to answering queries in theories using the Closed-World Assumption and its generalizations. Similarly, since prioritized circumscription is equivalent to a conjunction of (parallel) circumscriptions, our algorithm can be used to answer queries in theories circumscribed by prioritized circumscription.