Sampling Query Feedback Restricted Repairs of Functional Dependency Violations: Complexity and Algorithm

Abstract

An inconsistent database is a database instance violating integrity constraints. A repair of an inconsistent database is a maximal consistent subset. Sampling from the repair space is an alternative approach meeting the needs of many applications. In this paper, we introduce a new class of repair, query feedback restricted repair, based on the feedback on user’s witness query. We first map out a complete picture of both data and combined complexities of repair existence problems under different cases to identify the intractable cases. Especially, we show that if the query is a projection or a union query, then the decision problem is NP-complete; Even worse, if the query is a conjunctive query, the decision problem becomes \(\Sigma_{2}^{\mathrm{P}}\)-complete. At last, we provide a random repair sampling algorithm when the witness query is a selection-join query, and it is still polynomial even under the combined complexity.