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.
Emp_id Emp_name Qualification Dept_id Salary
E1
Raja
B.E
CS11
12000
E2
Rani
M.E
MS11 24000
• 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
Emp_id Dept_id Salary
E1
CS11
12000
E2
MS11
24000
emp2
Emp_id Emp_name Qualification
E1
Raja
B.E
E2
Rani
M.E
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