The Complexity of Ontology-Based Data Access with OWL 2 QL and Bounded Treewidth Queries

Abstract : Our concern is the overhead of answering OWL 2 QL ontology-mediated queries (OMQs) in ontology-based data access compared to evaluating their underlying tree-shaped and bounded treewidth conjunctive queries (CQs). We show that OMQs with bounded-depth ontologies have nonrecursive datalog (NDL) rewritings that can be constructed and evaluated in LOGCFL for combined complexity, even in NL if their CQs are tree-shaped with a bounded number of leaves, and so incur no overhead in complexity-theoretic terms. For OMQs with arbitrary ontologies and bounded-leaf CQs, NDL-rewritings are constructed and evaluated in LOGCFL. We show experimentally feasibility and scalability of our rewritings compared to previously proposed NDL-rewritings. On the negative side, we prove that answering OMQs with tree-shaped CQs is not fixed-parameter tractable if the ontology depth or the number of leaves in the CQs is regarded as the parameter, and that answering OMQs with a fixed ontology (of infinite depth) is NP-complete for tree-shaped and LOGCFL for bounded-leaf CQs.
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https://hal.inria.fr/hal-01632638
Contributor : Meghyn Bienvenu <>
Submitted on : Friday, November 10, 2017 - 2:40:38 PM
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Meghyn Bienvenu, Stanislav Kikot, Roman Kontchakov, Vladimir Podolskii, Vladislav Ryzhikov, et al.. The Complexity of Ontology-Based Data Access with OWL 2 QL and Bounded Treewidth Queries. PODS: Principles of Database Systems, Jun 2017, Chicago, United States. ⟨hal-01632638⟩

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