Query Answering under Non-guarded Rules in Datalog+/-

  • Andrea Calì
  • Georg Gottlob
  • Andreas Pieris
Part of the Lecture Notes in Computer Science book series (LNCS, volume 6333)


In ontology-based data access, an extensional database is enhanced by an ontology that generates new intensional knowledge which has to be considered when answering queries. In this setting, tractable data complexity (i.e., complexity w.r.t. the data only) of query answering is crucial, given the need to deal with large data sets. A well-known class of tractable ontology languages is the DL-lite family; however, in DL-lite it is impossible to express simple and useful integrity constraints that involve joins. To overcome this limitation, the Datalog+/- class of decidable languages uses tuple-generating dependencies (TGDs) as rules, thus allowing for conjunctions of atoms in the rule bodies, with suitable limitations to ensure decidability. In particular, sticky sets of TGDs allow for joins and variable repetition in rule bodies under certain conditions. In this paper we extend the notion of stickiness by introducing weakly-sticky sets of TGDs, which also generalize the well-known weakly-acyclic sets of TGDs. We investigate the complexity of query answering under such language, and in addition we provide novel complexity results on weakly-acyclic sets of TGDs. Moreover, we present the novel class of sticky-join sets of TGDs, which generalizes both sticky sets of TGDs and so-called linear TGDs, an extension of inclusion dependencies.


Turing Machine Schema Mapping Description Logic Dependency Graph Conjunctive Query 
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 2010

Authors and Affiliations

  • Andrea Calì
    • 3
    • 2
  • Georg Gottlob
    • 1
    • 2
  • Andreas Pieris
    • 1
  1. 1.Computing LaboratoryUniversity of OxfordUK
  2. 2.Oxford-Man Institute of Quantitative FinanceUniversity of OxfordUK
  3. 3.Department of Information Systems and ComputingBrunel UniversityUK

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