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

Meghyn Bienvenu (1) , Stanislav Kikot (2) , Roman Kontchakov (2) , Vladimir V Podolskii (3, 4) , Vladislav Ryzhikov (5) , Michael Zakharyaschev (2)

1 GRAPHIK - Graphs for Inferences on Knowledge
2 Birkbeck College [University of London]
3 SMI | RAS - Steklov Mathematical Institute [Moscow]
4 HSE - Vysšaja škola èkonomiki = National Research University Higher School of Economics [Moscow]
5 Free University of Bozen-Bolzano

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.

Mots clés: Ontology-based data access; Ontology-mediated query answering; Query rewriting; Parameterised complexity

Domaines: Base de données [cs.DB]; Intelligence artificielle [cs.AI]

Meghyn Bienvenu, Stanislav Kikot, Roman Kontchakov, Vladimir V 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⟩