Friday, 9 December 2016

What is partial functional dependency in dbms

Partial functional dependency / What is partial functional dependency / Why it is called as partial functional dependency? / Define partial functional dependency

Partial Functional Dependency

A functional dependency A  B is said to be partial if removal of any subset of A still able to recognize B uniquely.  

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.

For example, in a functional dependency PQ R, if either P alone or Q alone can uniquely identify R, then this is said to be Partial Functional Dependency. We read this as R is partially functionally dependent on P or R is partially functionally dependent on Q.

Another example: Assume the set of FDs for a relation Student as follows;
F = {regno name, regno dob, {regno, phone} gender, regno gender}

Here, in FD {regno, phone} gender, the attribute gender is partially dependent on regno attribute or left hand side. Here, phone is not required to identify gender uniquely.

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