Fourth normal form | normalization and its type

FOURTH  NORMAL FORM(4NF)

A relation is said to be in  fourth normal form, if the following conditions hold.

1.) A relation should be in  BCNF (or 3NF).

2.) It contains no multi-valued dependency.

EXAMPLE- Consider a relation "EMPLOYEE".In this relation all the three attributes act as a primary key since no single attribute can uniquely identify a tuple (record).

Empname	Equipment	Language
Anurag	PC	English
Anurag	PC	French
Anurag	Mainframe	English
Anurag	Mainframe	French
Kapil	PC	English
Kapil	PC	French
Kapil	PC	Japanese

In the above example relationship between Empname and Equipment is a multi-valued dependency.Thus it implies that

Similarly, the relationship between Empname and Language is a multi-valued dependency which is represented as  

So,the relation is not in 4NF .To make it into 4NF we have to remove all the multi-valued dependency.For that move each MVD (Multi-valued dependency)  pair to a new relation having relation names  EMP_GPP and EMP_APP.

Relation EMP_GPP-                                                                      

Empname	Equipment
Anurag	PC
Anurag	Mainframe
Kapil	PC

Relation EMP_APP-

Empname	Language
Anurag	English
Anurag	French
Kapil	English
Kapil	French
Kapil	Japanese

Now it is in 4NF.