31271 Lecture Notes - Lecture 6: Candidate Key, Third Normal Form, Foreign Key

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4 Jun 2018

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Lecture 6: Normalisation II

Boyce Codd Normal Form (BCNF)

• For a relation to be in BCNF, it must already be in third normal form, and every

determinant must be a candidate key.

• Put simply, a relation is not in BCNF if:

o A non-key functionally determines part of a key.

o Part of a key functionally determines part of a key.

• If the left side of a FD does not equate to a candidate key, it violates BCNF

Creating New Relations in a Higher Normal Form

1. Create a new relation for the FD group causing a violation

2. Create another new relation corresponding to the original relation

3. Copy the PK of the original relation to this new relation as its primary key

4. Move the dependencies (RHS) of the chosen FD in step one out of the original

relation into the new relation, as its non-key attributes.

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