First-Order Query Rewriting for Inconsistent Databases

We consider the problem of retrieving consistent answers over databases that might be inconsistent with respect to some given integrity constraints. In particular, we concentrate on sets of constraints that consist of key dependencies. Most of the existing work has focused on identifying intractable cases of this problem. In contrast, in this paper we give an algorithm that computes the consistent answers for a large and practical class of conjunctive queries. Given a query q, the algorithm returns a first-order query Q (called a query rewriting) such that for every (potentially inconsistent) database I, the consistent answers for q can be obtained by evaluating Q directly on I.