Towards Efficient Reasoning Under Guarded-Based Disjunctive Existential Rules

Pierre Bourhis, Michael Morak, Andreas Pieris

Research output: Chapter in Book/Report/Conference proceedingChapter


The complete picture of the complexity of answering (unions of) conjunctive queries under the main guarded-based classes of disjunctive existential rules has been recently settled. It has been shown that the problem is very hard, namely 2ExpTime-complete, even for fixed sets of rules expressed in lightweight formalisms. This gives rise to the question whether its complexity can be reduced by restricting the query language. Several subclasses of conjunctive queries have been proposed with the aim of reducing the complexity of classical database problems such as query evaluation and query containment. Three of the most prominent subclasses of this kind are queries of bounded hypertree-width, queries of bounded treewidth and acyclic queries. The central objective of the present paper is to understand whether the above query languages have a positive impact on the complexity of query answering under the main guarded-based classes of disjunctive existential rules.
We show that (unions of) conjunctive queries of bounded hypertree-width and of bounded treewidth do not reduce the complexity of our problem, even if we focus on predicates of bounded arity, or on fixed sets of disjunctive existential rules. Regarding acyclic queries, although our problem remains 2ExpTime-complete in general, in some relevant settings the complexity reduces to ExpTime-complete; in fact, this requires to bound the arity of the predicates, and for some expressive guarded-based formalisms, to fix the set of rules.
Original languageEnglish
Title of host publicationMathematical Foundations of Computer Science 2014
Subtitle of host publication39th International Symposium, MFCS 2014, Budapest, Hungary, August 25-29, 2014. Proceedings, Part I
EditorsErzsébet Csuhaj-Varjú, Martin Dietzfelbinger, Zoltán Ésik
Place of PublicationBerlin, Heidelberg
PublisherSpringer Berlin Heidelberg
Number of pages12
ISBN (Electronic)978-3-662-44522-8
ISBN (Print)978-3-662-44521-1
Publication statusPublished - 2014

Publication series

NameLecture Notes in Computer Science
PublisherSpringer Berlin Heidelberg
ISSN (Print)0302-9743


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