Canonical cover

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

The set has two important properties:

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

A canonical cover is not unique for a given set of functional dependencies, therefore one set F can have multiple covers .

Algorithm for computing a canonical cover[edit]

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



  1. ^ Silberschatz, Abraham (2011). Database system concepts (PDF) (Sixth ed.). New York: McGraw-Hill. ISBN 978-0073523323.