Functional dependency
From Wikipedia, the free encyclopedia.

A functional dependency is a constraint between two sets of attributes from a database.

An attribute X is said to functionally determine another attribute Y (X->Y) if and only if each X value is associated with precisely one Y value.

So if we are given the value of X we can determine the value of Y.

The original article can be found at: http://en.wikipedia.org/wiki/Functional_dependency.
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