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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.

ABC
a1b1c1
a1b1c2
a2b1c1
a2b1c3

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 : 

 

PQRST
12345
23456
34456

 

Reference Link

Fourth Normal Form (4NF)