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Normalization and optimization of schema mappings

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Abstract

Schema mappings are high-level specifications that describe the relationship between database schemas. They are an important tool in several areas of database research, notably in data integration and data exchange. However, a concrete theory of schema mapping optimization including the formulation of optimality criteria and the construction of algorithms for computing optimal schema mappings is completely lacking to date. The goal of this work is to fill this gap. We start by presenting a system of rewrite rules to minimize sets of source-to-target tuple-generating dependencies. Moreover, we show that the result of this minimization is unique up to variable renaming. Hence, our optimization also yields a schema mapping normalization. By appropriately extending our rewrite rule system, we also provide a normalization of schema mappings containing equality-generating target dependencies. An important application of such a normalization is in the area of defining the semantics of query answering in data exchange, since several definitions in this area depend on the concrete syntactic representation of the mappings. This is, in particular, the case for queries with negated atoms and for aggregate queries. The normalization of schema mappings allows us to eliminate the effect of the concrete syntactic representation of the mapping from the semantics of query answering. We discuss in detail how our results can be fruitfully applied to aggregate queries.

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Authors and Affiliations

  1. Computing Laboratory, Oxford University, Room 358, Wolfson Building, Parks Road, Oxford, OX1 3QD, United Kingdom

    Georg Gottlob

  2. Database and Artificial Intelligence Group, Institute of Information Systems, Vienna University of Technology, Favoritenstrasse 9, 1040, Vienna, Austria

    Reinhard Pichler & Vadim Savenkov

Authors
  1. Georg Gottlob
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  2. Reinhard Pichler
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  3. Vadim Savenkov
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Correspondence to Vadim Savenkov.

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Gottlob, G., Pichler, R. & Savenkov, V. Normalization and optimization of schema mappings. The VLDB Journal 20, 277–302 (2011). https://doi.org/10.1007/s00778-011-0226-x

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  • DOI: https://doi.org/10.1007/s00778-011-0226-x

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