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Third normal form (3NF)
- Third normal form:
- A relation is in third normal form if it is in 2NF and no non key attribute is transitively dependent on the primary key.
A bank uses the following relation:
Vendor(ID, Name, Account_No, Bank_Code_No, Bank)
The attribute ID is the identification key. All attributes are single
valued (1NF). The table is also in 2NF.
The following dependencies exist:
1. Name, Account_No, Bank_Code_No are functionally dependent on ID
(ID --> Name, Account_No, Bank_Code_No)
2. Bank is functionally dependent on Bank_Code_No (Bank_Code_No
--> Bank)
Example Third normal formThe table in this example is in 1NF and in 2NF. But there is a transitive dependency between Bank_Code_No and Bank, because Bank_Code_No is not the primary key of this relation. To get to the third normal form (3NF), we have to put the bank name in a separate table together with the clearing number to identify it.
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