Approximate Rewriting of Queries Using Views

  • Authors:

  • Foto Afrati;Manik Chandrachud;Rada Chirkova;Prasenjit Mitra

  • Affiliations:

  • National Technical University of Athens,;Computer Science Department, NC State University, Raleigh, USA;Computer Science Department, NC State University, Raleigh, USA;College of Information Sciences and Technology, Pennsylvania State University, USA

  • Venue:
  • ADBIS '09 Proceedings of the 13th East European Conference on Advances in Databases and Information Systems
  • Year:
  • 2009

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Abstract

We study approximate, that is contained and containing, rewritings of queries using views. We consider conjunctive queries with arithmetic comparisons (CQACs), which capture the full expressive power of SQL select-project-join queries. For contained rewritings, we present a sound and complete algorithm for constructing, for CQAC queries and views, a maximally-contained rewriting (MCR) whose all CQAC disjuncts have up to a predetermined number of view literals. For containing rewritings, we present a sound and efficient algorithm pruned-MiCR, which computes a CQAC containing rewriting that does not contain any other CQAC containing rewriting (i.e., computes a minimally containing rewriting, MiCR) and that has the minimum possible number of relational subgoals. As a result, the MiCR rewriting produced by our algorithm may be very efficient to execute. Both algorithms have good scalability and perform well in many practical cases, due to their extensive pruning of the search space, see [1].