Abstract :
This article deals with the computation of consistent answers to queries on relational databases that violate primary key constraints. A repair of such inconsistent database is obtained by selecting a maximal number of tuples from each relation without ever selecting two distinct tuples that agree on the primary key. We are interested in the following problem: Given a Boolean conjunctive query q, compute a Boolean first-order (FO) query image such that for every database image, image evaluates to true on image if and only if q evaluates to true on every repair of image. Such image is called a consistent FO rewriting of q.
We use novel techniques to characterize classes of queries that have a consistent FO rewriting. In this way, we are able to extend previously known classes and discover new ones. Finally, we use an Ehrenfeucht–Fraïssé game to show the non-existence of a consistent FO rewriting for image, where c is a constant and the first coordinate of R is the primary key.
