Fourth Normal Form (4NF) 

A relation schema r(R) is in 4NF with respect to a set D of Functional and multivalued dependencies if, for all multivalued Dependencies in D+ of the form α ➡➡  β,  where α ⊆ R and β ⊆ R, at least one of the following is true.

1. α ➡➡  β  is a trivial MVD.
2. α  is a super key for R.

More Normal Forms :

1. There is one more type of dependency called ‘Join Dependencies’.
2. These Join dependencies lead to another normal form called ‘Project-Join Normal Form’.
3. This PJNF is also called ‘Fifth Normal Form’.
4. There is one more type of normal form called ‘Domain-Key Normal Form’.

Example-1: Show all the functional dependencies of the following relation.

Example-2: Consider the following relation.

                             S = ( P, Q, R, S, T)

              S1 = ( P, Q, R)          S2 = ( R, S, T)   

Give an example of a relation, which says that the above relation is NOT loss-less decomposition.

Solution : 

Reference Link

Fourth Normal Form (4NF)