First Order-Rewritability and Containment of Conjunctive Queries in Horn Description Logics

TL;DR

This paper investigates the conditions and complexity of rewriting conjunctive queries into first-order logic within certain description logics, revealing that complexity varies with query type and logic features.

Contribution

It provides characterizations and complexity results for FO-rewritability and containment of conjunctive queries in a range of description logics, highlighting the impact of inverse roles.

Findings

FO-rewritability complexity ranges from ExpTime to 2ExpTime.

Inverse roles increase complexity for conjunctive queries.

Complexity differs between atomic and conjunctive queries.

Abstract

We study FO-rewritability of conjunctive queries in the presence of ontologies formulated in a description logic between EL and Horn-SHIF, along with related query containment problems. Apart from providing characterizations, we establish complexity results ranging from ExpTime via NExpTime to 2ExpTime, pointing out several interesting effects. In particular, FO-rewriting is more complex for conjunctive queries than for atomic queries when inverse roles are present, but not otherwise.