Query rewriting and answering under constraints in data integration systems

In this paper we address the problem of query answering and rewriting in global-as-view data integration systems, when key and inclusion dependencies are expressed on the global integration schema. In the case of sound views, we provide sound and complete rewriting techniques for a maximal class of constraints for which decidability holds. Then, we introduce a semantics which is able to cope with violations of constraints, and present a sound and complete rewriting technique for the same decidable class of constraints. Finally, we consider the decision problem of query answering and give decidability and complexity results.