An entity is in Third Normal Form if it is in Second Normal Form and each non-key attribute is dependent on the primary key and only on the primary key. Non-key attributes are not derived and are not dependent on other non-key attributes.

System Architect examines the primary keys associated with each non-key attribute. If it finds more than one entity having non-key attributes that are derived from the same data, it checks to see if the keys in the first entity are derived from the same data as a non-key attribute in the second entity.

ORDER LINE ITEM is in violation of 3NF because the attribute “TOTAL PRICE” is derived from the sum of “ORDER PRICE”, TAX, AND “SHIPPING CHARGE”. This kind of violation is not detected by SA; it must be found by the designer who understands the system under design.

ORDER FORM is in violation because the attribute “CUSTOMER NAME” is dependent on “CUSTOMER ID”. This type of violation is also referred to as a violation of Boyce-Codd Normal Form.