perkthim 4

Third Normal Form - 3NF Recall that an entity type is 3NF when it is 2NF and all its attributes are directly dependent on its primary key. A better way to word this rule is that the attributes (columns) of an entity type (table) must depend on all parts of the primary key. Therefore, 3NF is only an issue for tables with composite primary keys:

In table [OrderPayment2NF], the payment-type description (i.e., Cash, Visa, etc) depends only on the payment type and not on the combination or Order ID and payment type attributes. To resolve this problem, [PaymentType3NF] was introduced as shown above. Note now that in [PaymentType3NF], PaymentDescription fully depends on PayementType.