Complexity of Answering Counting Aggregate Queries Over DL-Lite

33 Pages Posted: 24 Jun 2018 Publication Status: Accepted

See all articles by Egor V. Kostylev

Egor V. Kostylev

University of Oxford; University of Edinburgh

Juan L. Reutter

Pontifical Catholic University of Chile


The ontology based data access model assumes that users access data by means of an ontology, which is often described in terms of description logics. As a consequence, languages for managing ontologies now need algorithms not only to decide standard reasoning problems, but also to answer database-like queries. However, fundamental database aggregate queries, such as the ones using functions COUNT and COUNT DISTINCT, have received very little attention in this context, and even defining appropriate semantics for their answers over ontologies appears to be a non-trivial task. Our goal is to study the problem of answering database queries with aggregation in the context of ontologies. This paper presents an intuitive semantics for answering counting queries, followed by a comparison with similar approaches that have been taken in different database contexts. Afterwards, it exhibits a thorough study of the computational complexity of evaluating counting queries conforming to this semantics.

Our results show that answering such queries over ontologies is decidable, but generally intractable. However, our semantics promotes awareness on the information that can be obtained by querying ontologies and raises the need to look for suitable approximations or heuristics in order to allow efficient evaluation of this widely used class of queries.

Keywords: Description Logics, OBDA, DL-Lite, Aggregate Queries, Count Queries, Complexity

Suggested Citation

Kostylev, Egor V. and Reutter, Juan L., Complexity of Answering Counting Aggregate Queries Over DL-Lite (2015). Journal of Web Semantics First Look 33_1_5, Available at SSRN: https://ssrn.com/abstract=3199190 or http://dx.doi.org/10.2139/ssrn.3199190

Egor V. Kostylev (Contact Author)

University of Oxford ( email )

Mansfield Road
Oxford, Oxfordshire OX1 4AU
United Kingdom

University of Edinburgh

Old College
South Bridge
Edinburgh, Scotland EH8 9JY
United Kingdom

Juan L. Reutter

Pontifical Catholic University of Chile ( email )

Av Libertador General Bernardo O'Higgins 340
Santiago, RegiĆ³n Metropolitana 8331150

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