Functional Dependency ( DBMS )

Functional Dependency :

The functional dependency is a relationship that exists between two attributes. It typically exists between the primary key and non-key attribute within a table.

X   →   Y The left side of FD is known as a determinant, the right side of the production is known as a dependent.

Types of Functional dependency :

·         Trivial functional dependency

·         Non-trivial functional dependency

Trivial functional dependency :

·         It is what one attribute determine to another Attribute.

 In a DBMS System.

E_No	E_Name	Salary	E_City
101	XYZ	10,000	Landon
102	PQR	20,000	Tokyo
103	ABC	30,000	Tokyo

• If We Know the “E_NO” We can Obtain “E_Name”, “E-City” and “Salary”.
• Functional Dependency is a Denoted By  ( → ) Arrow.
• It is a SET of Attribute, Which are call by “Trivial”. If the SET of Attribute are included in that attributes.

A = { E_No, City }
B = {E_No }
B  →  A

2. Non-trivial functional dependency :

·         A → B has a non-trivial functional dependency if B is not a subset of A.

·         When A intersection B is NULL, then A → B is called as complete non-trivial.

Example:

ID   →    Name, 

Name   →    DOB