Boyce-Codd Normal Form (BCNF)
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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