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From Wiki Notes @ WuJiewen.com, by Jiewen Wu
Revision as of 13:06, 5 August 2010 by Admin (talk | contribs) (Functional Dependency (FD))

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Functional Dependency (FD)

A FD, an integrity constraint, on a relation scheme R is a constraint X->Y, where X and Y are sets of attributes. For a pair of tuple t and s, they satisfies the above FD if they agree on all attributes in Y whenever they agree on all attributes in X.

Some properties of FDs.

  • Trivial (Reflexive) FDs: X->Y if Y is a subset of X.
  • Augmentation: if X->Y then XZ->YZ
  • Transitivity: if X->Y and Y->Z, then X->Z.
  • Union: if X->Y and X->Z, then X->YZ.
  • Decomposition: if X->YZ, then X->Y and X->Z.