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Term in database normalization From Wikipedia, the free encyclopedia
Second normal form (2NF), in database normalization, is a normal form. A relation is in the second normal form if it fulfills the following two requirements:
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Put simply, a relation (or table) is in 2NF if:
If any regular (non-prime) attributes are predictable (dependent) on another (non-prime) attribute, that is addressed in third normal form.
The second normal form was originally defined by E. F. Codd in 1971.[1]
To make a 1NF relation a 2NF relation, remove the functionally dependent attributes in the partial dependencies of the first normal form relation, and place those partial dependency dependent attributes in a relation where their corresponding determinant attributes are an entire candidate key.
The following relation does not satisfy 2NF because:
In other words, since {Manufacturer country} is a non-prime attribute functionally dependent on a proper subset of a candidate key, the relation is in violation of 2NF.
Manufacturer | Model | Manufacturer country |
---|---|---|
Forte | X-Prime | Italy |
Forte | Ultraclean | Italy |
Dent-o-Fresh | EZbrush | USA |
Brushmaster | SuperBrush | USA |
Kobayashi | ST-60 | Japan |
Hoch | Toothmaster | Germany |
Hoch | X-Prime | Germany |
To make the design conform to 2NF, it is necessary to have two relations. To create these relations:
As seen below, {Manufacturer country} is removed from the original table:
Manufacturer | Model |
---|---|
Forte | X-Prime |
Forte | Ultraclean |
Dent-o-Fresh | EZbrush |
Brushmaster | SuperBrush |
Kobayashi | ST-60 |
Hoch | Toothmaster |
Hoch | X-Prime |
As seen below, the partial dependency is put into a new relation where the dependency can exist without being a partial dependency:
Manufacturer | Manufacturer country |
---|---|
Forte | Italy |
Dent-o-Fresh | USA |
Brushmaster | USA |
Kobayashi | Japan |
Hoch | Germany |
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