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.
- α ➡➡ β is a trivial MVD.
- α is a super key for R.
More Normal Forms :
- There is one more type of dependency called ‘Join Dependencies’.
- These Join dependencies lead to another normal form called ‘Project-Join Normal Form’.
- This PJNF is also called ‘Fifth Normal Form’.
- 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.