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    The complexity of ontology-based data access with OWL 2 QL and bounded treewidth queries

    Bienvenu, M. and Kikot, Stanislav and Kontchakov, Roman and Podolskii, V.V. and Ryzhikov, V. and Zakharyaschev, Michael (2017) The complexity of ontology-based data access with OWL 2 QL and bounded treewidth queries. In: UNSPECIFIED (ed.) Proceedings of the 36th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems - PODS '17. New York, U.S.: Associating for Computing Machinery, pp. 201-216. ISBN 9781450341981.

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    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, more generally, 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, and even in NL if their CQs are tree-shaped with a bounded number of leaves. Thus, such OMQs incur no overhead in complexity-theoretic terms. For OMQs with arbitrary ontologies and bounded-leaf tree-shaped CQs, NDL-rewritings are constructed and evaluated in LOGCFL. We experimentally demonstrate 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 CQs and LOGCFL-complete for bounded-leaf CQs.

    Metadata

    Item Type: Book Section
    Additional Information: PODS '17 Proceedings of the 36th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems
    Depositing User: Administrator
    Date Deposited: 04 Sep 2017 13:59
    Last Modified: 04 Sep 2017 13:59
    URI: http://eprints.bbk.ac.uk/id/eprint/19408

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