Answering Path Queries under Linear and Guarded Existential Rules

[Submitted on 22 Jun 2026 (v1), last revised 24 Sep 2026 (this version, v2)]

Authors:Jean-François Baget (LIRMM, Inria, University of Montpellier, CNRS, France), Meghyn Bienvenu (Univ. Bordeaux, CNRS, Bordeaux INP, LaBRI, France), Marie-Laure Mugnier (LIRMM, Inria, University of Montpellier, CNRS, France), Michaël Thomazo (Inria, DIENS, ENS, PSL University, CNRS, France)

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Abstract:Ontology-mediated query answering is concerned with the problem of answering queries over knowledge bases consisting of a database instance and an ontology. While most work in the area focuses on conjunctive queries (CQs), navigational queries have gained increasing attention. In this paper, we investigate the complexity of answering two-way (conjunctive) regular path queries ((C)RPQs) over knowledge bases whose ontology is given by a set of guarded existential rules. We first consider the subclass of linear existential rules and show that (C)RPQ answering is NL-complete in data complexity, which matches the data complexity of answering RPQs over plain graph databases (i.e., without an ontology). In combined complexity, both tasks are ExpTime-complete in the general case, but RPQ and CRPQ answering drop to PTime-complete and PSpace-complete respectively if there is a bound on predicate arity. For guarded rules, we provide a non-trivial reduction to the linear case, which allows us to show that the complexity of (C)RPQ answering is the same as for CQs, namely 2ExpTime-complete in combined complexity (ExpTime-complete in the bounded-arity case) and PTime-complete in data complexity.

Submission history

From: Michaël Thomazo [view email]
[v1] Mon, 22 Jun 2026 09:34:08 UTC (113 KB)
[v2] Thu, 24 Sep 2026 14:57:00 UTC (111 KB)