A Dichotomy on the Complexity of Consistent Query Answering for Atoms with Simple Keys

Abstract

We study the problem of consistent query answering under primary key violations. In this setting, the relations in a database violate the key constraints and we are interested in maximal subsets of the database that satisfy the constraints, which we call repairs. For a boolean query Q, the problem CERTAINTY(Q) asks whether every such repair satisfies the query or not; the problem is known to be always in coNP for conjunctive queries. However, there are queries for which it can be solved in polynomial time. It has been conjectured that there exists a dichotomy on the complexity of CERTAINTY(Q) for conjunctive queries: it is either in PTIME or coNP-complete. In this paper, we prove that the conjecture is indeed true for the case of conjunctive queries without self-joins, where each atom has as a key either a single attribute (simple key) or all attributes of the atom.

Cited by in corpus (4)

• Dichotomies in Ontology-Mediated Querying with the Guarded Fragment
• A Trichotomy in the Data Complexity of Certain Query Answering for Conjunctive Queries
• Tractable vs. Intractable Cases of Matching Dependencies for Query Answering under Entity Resolution
• Consistent Answers of Conjunctive Queries on Graphs