Boyce-Codd Normal Form (BCNF)

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Boyce Codd Normal Form is introduced by Raymond F. Boyce and E.F. Codd based on Functional Dependency. BCNF definition is "a table is in Boyce-Codd normal form if and only if for every one of its non-trivial functional dependencies X hold Y, X is a superkey that is, X is either a candidate key or a superset thereof."

BCNF is used to eliminate non-trivial dependencies between candidate key attributes from one entity that attributes moved into external entity to avoid update, insert and delete anomalies.

An instance, an Employee_Contact_Information entity is maintains data through Emp_Code, Emp_Name, Address, City_Name, Postal_Code and Contact_Number attributes. The Emp_Code, City_Name, Postal_Code are prime attributes in the table is in 3NF.

The combination of {Emp_Code, City_Name, Postal_Code} is superkey and {Emp_Code, City_Name} or {Emp_Code, Postal_Code} is candidate key of Employee_Contact_Information entity. The non-trivial functional dependency is {Emp_Code, City_Name} hold {Postal_Code} that {Postal_Code} hold {City_Name} attribute's data.

According to the BCNF, the City_Name attribute can move into external Postal_City entity to avoid redundant data. The decomposed Employee_Contact_Information entity can relate with Postal_City entity through common Postal_Code attribute and Referential Integrity Constraints.

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