Parallel-Correctness and Containment for Conjunctive Queries with Union and Negation

TL;DR

This paper investigates the complexity of parallel correctness for unions of conjunctive queries with negation, extending existing theories and establishing that containment with negation is coNEXPTIME-complete.

Contribution

It extends the analysis of parallel correctness to queries with negation and unions, and proves the coNEXPTIME-completeness of containment for such queries.

Findings

Parallel correctness analysis extended to queries with negation and unions.

Containment problem for conjunctive queries with negation is coNEXPTIME-complete.

Insights into the complexity of parallel query evaluation in distributed systems.

Abstract

Single-round multiway join algorithms first reshuffle data over many servers and then evaluate the query at hand in a parallel and communication-free way. A key question is whether a given distribution policy for the reshuffle is adequate for computing a given query, also referred to as parallel-correctness. This paper extends the study of the complexity of parallel-correctness and its constituents, parallel-soundness and parallel-completeness, to unions of conjunctive queries with and without negation. As a by-product it is shown that the containment problem for conjunctive queries with negation is coNEXPTIME-complete.