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Query evaluation with null values: How complex is completeness?

  • Complexity And Analysis Of Algorithms
  • Conference paper
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Foundations of Software Technology and Theoretical Computer Science (FSTTCS 1989)

Part of the book series: Lecture Notes in Computer Science ((LNCS,volume 405))

Abstract

The problem of evaluating queries on a relational database which is allowed to contain null values has been extensively studied. In general, most of the approaches to query evaluation in the literature seem to fall into two categories. Those in the first guarantee that answers to queries can be efficiently computed (i.e. in time polynomial in the database size), while being “incomplete” in the sense that they do not compute all “valid” answers to certain queries. The second kind guarantee “completeness” but unfortunately suffer from intractability. In this paper, we reexamine the proof-theoretic approach proposed by Reiter [Re 86] (which as proposed is incomplete) and present a “natural” interpretation of null values based on various possible null assignments. We show that this approach leads to completeness of query evaluation. We bring out the drawback of such an extension by showing that evaluation of even “simple” queries using this approach is co-NP-complete. We then propose an approach based on intuitionistic logic for the problem. The advantages are that query evaluation is now guaranteed to be complete (w.r.t. the new approach) and computable in time polynomial in the database size.

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Author notes

  1. V. S. Lakshmanan

    Present address: Concordia University, Montreal, Canada

Authors and Affiliations

  1. Department of Computer Science, University of Toronto, M5S 1A4, Toronto, Canada

    V. S. Lakshmanan

Authors
  1. V. S. Lakshmanan
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Editor information

C. E. Veni Madhavan

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© 1989 Springer-Verlag Berlin Heidelberg

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Lakshmanan, V.S. (1989). Query evaluation with null values: How complex is completeness?. In: Veni Madhavan, C.E. (eds) Foundations of Software Technology and Theoretical Computer Science. FSTTCS 1989. Lecture Notes in Computer Science, vol 405. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-52048-1_45

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  • DOI: https://doi.org/10.1007/3-540-52048-1_45

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  • Publisher Name: Springer, Berlin, Heidelberg

  • Print ISBN: 978-3-540-52048-1

  • Online ISBN: 978-3-540-46872-1

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