A Dichotomy in the Complexity of Consistent Query Answering for Two Atom Queries With Self-Join

TL;DR

This paper proves that the complexity of consistent query answering for two-atom queries with self-join under primary key constraints follows a clear dichotomy, being either polynomial or coNP-complete, extending previous results.

Contribution

It extends the dichotomy conjecture verification to include two-atom queries with self-joins, previously verified only for self-join-free and path queries.

Findings

Dichotomy holds for two-atom queries with self-joins.

Complexity is either polynomial or coNP-complete.

Extends previous results to a broader class of queries.

Abstract

We consider the dichotomy conjecture for consistent query answering under primary key constraints. It states that, for every fixed Boolean conjunctive query q, testing whether q is certain (i.e. whether it evaluates to true over all repairs of a given inconsistent database) is either polynomial time or coNP-complete. This conjecture has been verified for self-join-free and path queries. We show that it also holds for queries with two atoms.