The third NORMAL form (3NF) is used for preventing data duplication and data abnormalities. A relation is said to have met the third normal form when there are no transitive dependencies for non-prime ATTRIBUTES as present in the second normal form. A 3NF relation is said to have achieved if any one of the below conditions are met for every non-trivial functional dependency A->B:

• A- super key
• B- prime attribute where every attribute is a part of candidate key

For a table to achieve 3NF form, it should first be in 1NF (First Normal Form) and achieve 2NF (Second Normal Form). The rows in the table should be dependent only on the KEYS. If the contents of fields apply to more than 1 primary key, then they should be put in another table.

For instance, if a patient’s records have a doctor’s phone number STORED with the patient’s details, it doesn’t meet the 3NF standards. Because the doctor’s number should be part of the doctor table for avoiding duplication in the patient table because a doctor can have more than one patient.