Description logics for semantic query optimization in object-oriented database systems

  • Authors:

  • Domenico Beneventano;Sonia Bergamaschi;Claudio Sartori

  • Affiliations:

  • Università di Modena e Reggio Emilia and CSITE--CNR, Modena, Italy;Università di Modena e Reggio Emilia and CSITE--CNR, Modena, Italy;Università di Bologna and CSITE--CNR, Bologna, Italy

  • Venue:
  • ACM Transactions on Database Systems (TODS)
  • Year:
  • 2003

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Abstract

Semantic query optimization uses semantic knowledge (i.e., integrity constraints) to transform a query into an equivalent one that may be answered more efficiently. This article proposes a general method for semantic query optimization in the framework of Object-Oriented Database Systems. The method is effective for a large class of queries, including conjunctive recursive queries expressed with regular path expressions and is based on three ingredients. The first is a Description Logic, ODLRE, providing a type system capable of expressing: class descriptions, queries, views, integrity constraint rules and inference techniques, such as incoherence detection and subsumption computation. The second is a semantic expansion function for queries, which incorporates restrictions logically implied by the query and the schema (classes + rules) in one query. The third is an optimal rewriting method of a query with respect to the schema classes that rewrites a query into an equivalent one, by determining more specialized classes to be accessed and by reducing the number of factors. We implemented the method in a tool providing an ODMG-compliant interface that allows a full interaction with OQL queries, wrapping underlying Description Logic representation and techniques to the user.