Advanced Database Management System - Tutorials and Notes: Partial Functional Dependency - Definition

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Sunday, 15 May 2016

Partial Functional Dependency - Definition


Partial Functional Dependency - Definition / What is Partial dependency? / Example for partial key dependency / Partial key functional dependency - an overview

Partial Dependency


Partial Dependency is a form of Functional dependency that holds on a set of attributes. It is about the complete dependency of a right hand side attribute on one of the left hand side attributes. In a functional dependency XY Z, if Z (RHS attribute) can be uniquely identified by one of the LHS attributes, then the functional dependency is partial dependency.

Example:
Let us assume a relation R with attributes A, B, C, and D. Also, assume that the set of functional dependencies F that hold on R as follows;
F = {A B, D C}.
From set of attributes F, we can derive the primary key. For R, the key can be (A,D), a composite primary key. That means, AD BC, AD can uniquely identify B and C. But, for this case A and D is not required to identify B or C uniquely. To identify B, attribute A is enough. Likewise, to identify C, attribute D is enough. The functional dependencies AD B or AD C are called as Partial functional dependencies.


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