First-Order Under-Approximations of Consistent Query Answers

Abstract

Consistent Query Answering (CQA) has by now been widely adopted as a principled approach for answering queries on inconsistent databases. The consistent answer to a query q on an inconsistent database \({\mathbf {db}}\) is the intersection of the answers to q on all repairs, where a repair is any consistent database that is maximally close to \({\mathbf {db}}\). Unfortunately, computing consistent answers under primary key constraints has already exponential data complexity for very simple conjunctive queries, which is completely impracticable.