Checking Chase Termination over Ontologies of Existential Rules with Equality

TL;DR

This paper investigates chase termination over ontologies with existential rules and equality, proposing a practical approach using acyclicity notions on axiomatised versions and introducing a new acyclicity concept for such ontologies.

Contribution

It introduces an efficient method for checking chase termination with equality by leveraging existing acyclicity notions on axiomatised ontologies and proposes a new acyclicity notion for direct application.

Findings

Applying acyclicity notions to axiomatisations improves efficiency

Chase terminates for original ontology if it terminates for any axiomatisation

Equality model-faithful acyclicity is a new applicable notion

Abstract

The chase is a sound and complete algorithm for conjunctive query answering over ontologies of existential rules with equality. To enable its effective use, we can apply acyclicity notions; that is, sufficient conditions that guarantee chase termination. Unfortunately, most of these notions have only been defined for existential rule sets without equality. A proposed solution to circumvent this issue is to treat equality as an ordinary predicate with an explicit axiomatisation. We empirically show that this solution is not efficient in practice and propose an alternative approach. More precisely, we show that, if the chase terminates for any equality axiomatisation of an ontology, then it terminates for the original ontology (which may contain equality). Therefore, one can apply existing acyclicity notions to check chase termination over an axiomatisation of an ontology and then use the original ontology for reasoning. We show that, in practice, doing so results in a more efficient reasoning procedure. Furthermore, we present equality model-faithful acyclicity, a general acyclicity notion that can be directly applied to ontologies with equality.