Relational Database Model

Third Normal Form (3NF)

Third Normal Form (3NF) is introduced by E.F. Codd based on Functional Dependency. E.F. Codd's definition is "a table is in 3NF if and only if both of the following conditions hold that the relation R (table) is in second normal form (2NF) and every non-prime attribute of R is not-transitively dependent on every key of R."

3NF is used to eliminate transitive dependency attributes from one entity that attributes moved into external entity to avoid update, insert and delete anomalies.

An instance, the 2NF Employee_Master entity is maintains transitive dependency data in the Designation_Name and Department_Name attributes. According to the 3NF, the Designation_Name and Department_Name attributes can move into external Designation_Master and Department_Master entities to avoid redundant data.

The decomposed Employee_Master entity can relate with Designation_Master and Department_Master entities through common Design_Code and Dept_Code attributes and Referential Integrity Constraints.

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