A table is said to be in the Third Normal Form, if all the non key fields of the table are independent of all other non key fields of the table.

A relation is in the third normal form if it is in second normal form and no non-prime attribute is functionally dependent on other non-prime attribute.

The 2NF tables we established in the previous section represent a significant improvement over 1NF tables.

However, they still suffer from the same types of anomalies as the 1NF tables although for different reasons associated with transitive dependencies.

If a transitive (functional) dependency exists in a table, it means that two separate facts are represented in that table, one fact for each functional dependency involving a different left side.

A table is in third normal form (3NF) if and only if for every nontrivial functional dependency X->A, where X and A are either simple or composite attributes, one of two conditions must hold.

Either attribute X is a superkey, or attribute A is a member of a candidate key.

If attribute A is a member of a candidate key, A is called a prime attribute.

A relation will be in 3NF if it is in 2NF and not contain any transitive partial dependency.

3NF is used to reduce the data duplication. It is also used to achieve the data integrity.

If there is no transitive dependency for non-prime attributes, then the relation must be in third normal form.