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Querying the Guarded Fragment with Transitivity

  • Georg Gottlob
  • Andreas Pieris
  • Lidia Tendera
Part of the Lecture Notes in Computer Science book series (LNCS, volume 7966)

Abstract

We study the problem of answering a union of Boolean conjunctive queries q against a database Δ, and a logical theory ϕ which falls in the guarded fragment with transitive guards (GF + TG). We trace the frontier between decidability and undecidability of the problem under consideration. Surprisingly, we show that query answering under GF2 + TG, i.e., the two-variable fragment of GF + TG, is already undecidable (even without equality), whereas its monadic fragment is decidable; in fact, it is 2exptime-complete in combined complexity and coNP-complete in data complexity. We also show that for a restricted class of queries, query answering under GF+TG is decidable.

Keywords

Description Logic Conjunctive Query Transitive Relation Ground Atom Query Answering 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • Georg Gottlob
    • 1
  • Andreas Pieris
    • 1
  • Lidia Tendera
    • 2
  1. 1.Department of Computer ScienceUniversity of OxfordUK
  2. 2.Institute of Mathematics and InformaticsOpole UniversityPoland

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