Encyclopedia of Database Systems

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

Functional Dependency

  • Solmaz Kolahi
Reference work entry
DOI: https://doi.org/10.1007/978-1-4614-8265-9_1247

Synonyms

FD

Definition

Given a relation schema R[U], a functional dependency (FD) 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, t1[X] = t2[X] implies t1[Y ] = t2[Y]. That is, whenever two tuples contain the same values for attributes in X, they must have the same values for attributes in Y. A functional dependency XY is called trivial if YX.

A key dependency is a functional dependency of the form XU. Then X is called a superkey for relation R. If there is no proper subset Y of X such that Y is a superkey, then X is called a key.

Key Points

Functional dependencies form an important class of integrity constraints that play a critical role in maintaining the integrity of data, query optimization and indexing, and especially schema design. The focus of the normalizationtechnique in schema design is on avoiding redundancies caused by functional and other types of dependencies...

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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