Query Answering in Circumscription

We address the problem of answering queries in circumscription and related nonmonotonic formalisms. The answering process we describe uses resolution-based theorem provers recently developed for circumscription. In a way analogous to query answering techniques in classical predicate logic, the process extracts information from a proof of the query. Circumscriptive theorem provers consist of two processes, generating explanations for the theorem to be proved and showing that these explanations cannot be refuted. In general, many explanations compete in supporting the theorem. We show that queries can be answered by finding certain combinations of explanations, and present results to search the space of explanations while carrying out significant pruning on this space. The results are relevant to other nonmonotonic formalisms having explanation-based proof procedures.