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Lesson Navigation IconRelational database model

Unit Navigation IconConcepts

Unit Navigation IconTransforming ER-schema

Unit Navigation IconData integrity

Unit Navigation IconNormalization

LO Navigation IconDependencies

LO Navigation IconFirst normal form (1NF)

LO Navigation IconSecond normal form (2NF)

LO Navigation IconThird normal form (3NF)

LO Navigation IconExercise normalization

LO Navigation IconUnit summary

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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 formExample Third normal form

The 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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