Complexity of Inconsistency−Tolerant Query Answering in Datalog+⁄− under Cardinality−Based Repairs

Abstract

Querying inconsistent ontological knowledge bases is an important problem in practice, for which several inconsistency-tolerant query answering semantics have been proposed, including query answering relative to all repairs, relative to the intersection of repairs, and relative to the intersection of closed repairs. In these semantics, one assumes that the input database is erroneous, and the notion of repair describes a maximally consistent subset of the input database, where different notions of maximality (such as subset and cardinality maximality) are considered. In this paper, we give a precise picture of the computational complexity of inconsistency-tolerant (Boolean conjunctive) query answering in a wide range of Datalog± languages under the cardinality-based versions of the above three repair semantics.