Fourth Normal Form (4NF)
Fourth normal form builds on the first three normal forms (1NF, 2NF and 3NF) and the Boyce-Codd Normal Form (BCNF).
In addition to a database meeting the requirements of BCNF, fourth normal form must not contain more than one multivalued dependency.This normal form handles multi-valued dependencies caused by 1NF. When we see repeated groups or multiple values in an intersection, we add additional tuples removing multiple values. That is what we do with 1NF. When there are two multi-value attributes in a relation, then each value in one of the attributes has to be repeated with every value of the other attribute.
| This situation is referred as a multi-valued dependency. The table shows an example of multi-valued dependency. |
|
| If we apply 1NF to the above relation, the table will become this: |
|