A unified apriori-like algorithm for conjunctive query containment

  • Authors:

  • Fang Wei;Georg Lausen

  • Affiliations:

  • University of Freiburg;University of Freiburg

  • Venue:
  • IDEAS '08 Proceedings of the 2008 international symposium on Database engineering & applications
  • Year:
  • 2008

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Abstract

The design of containment checking algorithms for conjunctive queries with arithmetic comparisons and safe negations (CQ­s) is fundamental to many database applications. However, it is a challenging task due to the intractability of the problem. Existing algorithms are either computationally too expensive, or capable to deal with only a fragment of these extensions. In this paper we propose a novel algorithm for testing containment of CQ­s. The key idea of the algorithm is to recursively consider only the containment mappings between the positive subgoals of the queries, instead of testing all the symbol mappings. Thus the number of test cases can be drastically reduced. Our algorithm enables further an on the fly execution of the normalization step. With the observation that the property of anti-monotonicity holds in our problem setting, we develop an Apriori-like algorithm as a sub-function of the containment checking algorithm, to which desirable pruning strategies are applied. Furthermore, we identify the criteria to reduce the number of test sets, and demonstrate that two additional improvements to the containment checking algorithm: node clustering and tuple pruning can further speed up the checking process.