Functional Dependency (FD) | Database design

FUNCTIONAL DEPENDENCY(FD)

An attribute of an relational 'R' is said to be functional dependent on attribute 'X' if and only if each 'X' value is associated with exactly one value of 'Y' at any given time.

REPRESENTATION-

Where 'X' is known as determinant and 'Y' is known as determined.

EXAMPLE-

HOW TO SHOW FUNCTIONAL DEPENDENCY DIAGRAMMATICALLY-

Consider a relation

S.NO	SNAME	DEPT	CITY
S1	A	10	X
S2	B	20	Y
S3	C	20	Y

Now find various functional dependencies which are

Represent this functional dependency diagrammatically

FULLY FUNCTIONAL DEPENDENCY-

An attribute 'Y' Of relation 'R' is fully functional dependent on attribute 'X' if it is function dependent on 'X' and not functionally dependent on any subset of 'X'.

                                                            When primary key is composite then the non key attributes must be identified by the entire key and not by some attributes.