Query answering under expressive entity-relationship schemata

  • Authors:

  • Andrea Calì;Georg Gottlob;Andreas Pieris

  • Affiliations:

  • Department of Information Systems and Computing, Brunel University, UK and Oxford-Man Institute of Quantitative Finance, University of Oxford, UK;Computing Laboratory, University of Oxford, UK and Oxford-Man Institute of Quantitative Finance, University of Oxford, UK;Computing Laboratory, University of Oxford, UK

  • Venue:
  • ER'10 Proceedings of the 29th international conference on Conceptual modeling
  • Year:
  • 2010

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Abstract

We address the problem of answering conjunctive queries under constraints representing schemata expressed in an extended version of the Entity-Relationship model. This extended model, called ER+ model, comprises is-a constraints among entities and relationships, plus functional and mandatory participation constraints. In particular, it allows arbitrary permutations of the roles in is-a among relationships. A key notion that ensures high tractability in ER+ schemata is separability, i.e., the absence of interaction between the functional participation constraints and the other constructs of ER+. We provide a precise syntactic characterization of separable ER+ schemata, called ER± schemata, by means of a necessary and sufficient condition. We present a complete complexity analysis of the conjunctive query answering problem under ER± schemata. We show that the addition of so-called negative constraints does not increase the complexity of query answering. With such constraints, our model properly generalizes the most widely-adopted tractable ontology languages.