Functional Dependency

If in a relation, one attribute determines another attribute uniquely, then we say that functional dependency has occurred. Functional Dependency can be written as

Above statement means Q is functionally dependent on P. P is known as determinant set and Q the dependent attribute.

Properties of Functional Dependencies

If A, B and C are sets of attributes in a relation R, then one of the important property are defined by Armstrong’s axioms, used for database normalization.

•    Axiom of Reflexivity: If B is a subset of A, then A → B.
•    Axiom of Augmentation: If A → B, then AC → BC.
•    Axiom of Transitivity: If A → B and B → C, then A → C.