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.