Girish Mahajan (Editor)

Canonical cover

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A canonical cover F c for F (a set of functional dependencies on a relation scheme) is a set of dependencies such that F logically implies all dependencies in F c , and F c logically implies all dependencies in F.

The set F c has two important properties:

  1. No functional dependency in F c contains an extraneous attribute.
  2. Each left side of a functional dependency in F c is unique. That is, there are no two dependencies a → b and c → d in F c such that a = c .

Algorithm for computing a canonical cover

  1. F c = F
  2. Repeat:
    1. Use the union rule to replace any dependencies in F c of the form a → b and a → d with a → b d ..
    2. Find a functional dependency in F c with an extraneous attribute and delete it from F c
  3. ... until F c does not change

References

Canonical cover Wikipedia
(Text) CC BY-SA


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