Encyclopedia of Database Systems

2018 Edition
| Editors: Ling Liu, M. Tamer Özsu

Multivalued Dependency

  • Solmaz Kolahi
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1248

Synonyms

MVD

Definition

A multivalued dependency (MVD) over a relation schema R[U], is an expression of the form XY, where X,YU. An instance I of R[U] satisfies XY, denoted by IXY, if for every two tuples t1, t2 in I such that t1[X] = t2[X], there is another tuple t3 in I such that t3[X] = t1[X] = t2[X], t3[Y ] = t1[Y], and t3[Z] = t2[Z], where Z = UXY (XY represents XY). In other words, for every value of X, the value of attributes in Y is independent of the value of attributes in Z. A multivalued dependencyXY is a special case of a join dependency expressed as ⋈[XY,X(UXY)], which specifies that the decomposition of any instance I satisfying ⋈ [XY,X(UXY)] into π XY (I) and π X(UXY)(I) is lossless, i.e., I = π XY (I) ⋈ π X(UXY)(I).

Key Points

Multivalued dependencies, like functional dependencies, can cause redundancy in relational databases. For instance, in the following table, each director of the movie The Matrixis recorded once per actor of the...

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Recommended Reading

  1. 1.
    Abiteboul S, Hull R, Vianu V. Foundations of databases. Reading: Addison-Wesley; 1995.zbMATHGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2018

Authors and Affiliations

  1. 1.University of British ColumbiaVancouverCanada

Section editors and affiliations

  • Leonid Libkin
    • 1
  1. 1.School of InformaticsUniversity of EdinburghEdinburghUK