Question

Write short notes on the following with suitable examples.

a. 4NF b. 5NF

Answer 1

a.

Any relation is said to be in the fourth normal form when it satisfies the following conditions:

• It must be in Boyce Codd Normal Form (BCNF is based on functional dependencies that take into account all candidate keys in a relation)
• It should have no multi-valued dependency. (A multi-valued dependency is said to occur when there are two attributes in a table which depend on a third attribute but are independent of each other)

b.

Any relation in order to be in the fifth normal form must satisfy the following conditions:

• It must be in Fourth Normal Form (4NF).
• It should have no join dependency and also the joining must be lossless.

In the fifth normal form the relation must be decomposed in as many sub-relations as possible so as to avoid any kind of redundancy and there must be no extra tuples generated when the sub-relations are combined together by using natural join.