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2011 IEEE 27th International Conference on Data Engineering (2011)
Hannover, Germany
Apr. 11, 2011 to Apr. 16, 2011
ISBN: 978-1-4244-8959-6
pp: 2-13
Georg Gottlob , Computing Laboratory, University of Oxford, UK
Giorgio Orsi , Computing Laboratory, University of Oxford, UK
Andreas Pieris , Computing Laboratory, University of Oxford, UK
Ontological queries are evaluated against an enterprise ontology rather than directly on a database. The evaluation and optimization of such queries is an intriguing new problem for database research. In this paper we discuss two important aspects of this problem: query rewriting and query optimization. Query rewriting consists of the compilation of an ontological query into an equivalent query against the underlying relational database. The focus here is on soundness and completeness. We review previous results and present a new rewriting algorithm for rather general types of ontological constraints (description logics). In particular, we show how a conjunctive query (CQ) against an enterprise ontology can be compiled into a union of conjunctive queries (UCQ) against the underlying database. Ontological query optimization, in this context, attempts to improve this process so to produce possibly small and cost-effective output UCQ. We review existing optimization methods, and propose an effective new method that works for Linear Datalog<sup>±</sup>, a description logic that encompasses well-known description logics of the DL-Lite family.

G. Gottlob, G. Orsi and A. Pieris, "Ontological queries: Rewriting and optimization," 2011 IEEE 27th International Conference on Data Engineering(ICDE), Hannover, Germany, 2011, pp. 2-13.
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