Efficient Fixpoint Methods for Approximate Query Answering in Locally Complete Databases

Standard databases convey Reiter’s closed-world assumption that an atom not in the database is false. This assumption is relaxed in locally complete databases that are sound but only partially complete about their domain. One of the consequences of the weakening of the closed-world assumption is that query answering in locally closed databases is not tractable. In this paper we develop efficient approximate methods for query answering, based on fixpoint computations. We present preliminary results for a broad class of locally closed databases in which this method produces complete answers to queries.