Containment of Simple Regular Path Queries

TL;DR

This paper investigates the complexity of query containment for Conjunctive Regular Path Queries (CRPQs), focusing on practical restricted fragments and providing a detailed complexity classification.

Contribution

It offers a comprehensive complexity analysis of CRPQ containment for various restricted fragments, including new completeness results.

Findings

Containment complexity varies from NP to EXPSPACE depending on query features.

Restricted fragments relevant in practice often have lower complexity.

The study maps features to their corresponding computational complexity classes.

Abstract

Testing containment of queries is a fundamental reasoning task in knowledge representation. We study here the containment problem for Conjunctive Regular Path Queries (CRPQs), a navigational query language extensively used in ontology and graph database querying. While it is known that containment of CRPQs is expspace-complete in general, we focus here on severely restricted fragments, which are known to be highly relevant in practice according to several recent studies. We obtain a detailed overview of the complexity of the containment problem, depending on the features used in the regular expressions of the queries, with completeness results for np, pitwo, pspace or expspace.