Second Normal Form or 2NF is based on the concept of full functional dependency.
Full Functional Dependency:
In a relation R, an attribute Q is said to be fully functional dependent on attribute P, if it is functionally dependent on P and not functionally dependent on any proper subset of P. The dependency P → Q is left reduced, their being no extraneous attributes in the left hand side of the dependency.
If AD → C, is fully functional dependency, then we cannot remove A or D. i.e. C is fully functional dependent on AD. If we are able to remove A or D, then it is not full functional dependency.
