Boyce-Codd Normal Form (BCNF)

Database Normalization Boyce-Codd Normal Form (BCNF) A relation is in Boyce-Codd normal form (BCNF) if every determinant in the table is a candidate key. (A determinant is any attribute whose value determines other values with a row.) If a table contains only one candidate key, the 3NF and the BCNF are equivalent. BCNF is a special case of 3NF.

Boyce-Codd Normal Form A relation schema R is in BCNF if whenever a non trivial functional dependency X A holds in R then X is a super key of R. BCNF is more rigorous from of 3NF. It deals with relational tables which has multiple candidate keys and composite candidate keys. BCNF is based on the concept of determinant. A determinant refers to the attribute or group of attributes on the left hand side of the arrow of the functional dependency ()

Example Unnormalized employee table. The employee table has 3 determinates : emp_id, deptid, qualification. But (emp_id, dept_id) is a candidate key. So this relation is not in BCNF. For a relation to be in BCNF each determinant must be a candidate key. Normalized employee table – employee table in BCNF. The employee table is split into emp1 & emp2 in BCNF

emp1 emp2 Emp1 has one determinant (empid,deptid), emp2 has one determinant (emp_id) so, emp1 and emp2 are in BCNF.

Example R = { branch_name, branch_city, branch_assets, Custome_name, Loan_number, loan_amount) F = { branch_name branch_assets, branch_city. Loan_numberloan_amount, branch_name} Key = {loan_number, customer_name} Decomposed to R1 = { branch_name, branch_city, branch_assets) R2 = { branch_name, Custome_name, Loan_number, loan_amount) R3 = { branch_name, Loan_number, loan_amount) R4 = {Custome_name, Loan_number, loan_amount) Final decomposition : R1, R3, R4

Sample Data for a BCNF Conversion

Decomposition into BCNF