Multi valued dependency | Database design

MULTI-VALUED DEPENDENCY(MVD)

DEFINITION- MVD's occurs when two or more independent multi-valued facts about some attribute occur within the same table. Multi-valued dependency represented as

                                         

defines a relationship in which set of values in attribute B are determined  by a single value of A.

EXAMPLE:- Consider a relation EMP .

              

Ename	Child	Salary	Grade
Ranjit	Sunny	25000	2012
Ranjit	Sunny	30000	2012
Pankaj	Akshay	15000	2013
Pankaj	Akshay	25000	2014
Pankaj	Rupa	15000	2013
Pankaj	Rupa	25000	2014

In the above example child is the multi-valued fact of Ename which means that corresponding to the employee name, we have multiple values of children. e.g. Ename pankaj has two values {Akshay,Rupa} corresponding to him at this particular instance of time or we can say child is multi-valued dependent on Ename.