Consistent query answering with prioritized active integrity constraints

Consistent query answering is a principled approach for querying inconsistent databases. It relies on two basic notions: the notion of a repair, that is, a consistent database that "minimally" differs from the original one, and the notion of a consistent query answer, that is, a query answer that can be derived from every repair. In general, an inconsistent database can admit multiple repairs, each corresponding to a different way of restoring consistency, and the consistent query answering framework does not make any discrimination among them. However, in many applications it is natural and desired to express preferences among the different choices that can be made to resolve inconsistency. In this paper, we consider the framework of Prioritized Active Integrity Constraints (PAICs), a declarative and powerful form of active rules which enable users to express a wide range of integrity constraints along with preferences on how consistency should be restored. PAICs induce preferences among repairs, so that a set of "preferred" ones can be identified. Then, "preferred" query answers are naturally defined as query answers derived from preferred repairs only. We show how preferred repairs can be obtained from the preferred stable models of a prioritized logic program derived from a given a set of PAICs. Furthermore, we study the restricted class of Prioritized Active Functional Dependencies (PAFDs), which admits a unique preferred repair and for which query answering can be accomplished in polynomial time.