An information-theoretic approach to normal forms for relational and XML data

  • Authors:

  • Marcelo Arenas;Leonid Libkin

  • Affiliations:

  • University of Toronto;University of Toronto

  • Venue:
  • Proceedings of the twenty-second ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
  • Year:
  • 2003

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Abstract

Normalization as a way of producing good database designs is a well-understood topic. However, the same problem of distinguishing well-designed databases from poorly designed ones arises in other data models, in particular, XML. While in the relational world the criteria for being well-designed are usually very intuitive and clear to state, they become more obscure when one moves to more complex data models.Our goal is to provide a set of tools for testing when a condition on a database design, specified by a normal form, corresponds to a good design. We use techniques of information theory, and define a measure of information content of elements in a database with respect to a set of constraints. We first test this measure in the relational context, providing information-theoretic justification for familiar normal forms such as BCNF, 4NF, PJ/NF, 5NFR, DK/NF. We then show that the same measure applies in the XML context, which gives us a characterization of a recently introduced XML normal form called XNF. Finally, we look at information-theoretic criteria for justifying normalization algorithms.