Page 144 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Unit 8: Normalization

Notes
Transaction Table
Tran_id Acc_id Tran_type Tan_mode Amount
14300 994 B/F 1000
14301 994 Deposit Bycash 1000
14302 994 Withdrawal ATM 500
14303 340 B/F 3500
14304 340 Deposit Payroll 3500
14305 340 Withdrawal ATM 1000
14306 699 B/F 6000
14307 699 Credit Bycash 2000
14308 699 Withdrawal ATM 6500

8.5 Boyce Codd Normal Form

The Boyce Codd Normal form is implemented in cases where the table has:
1. Multiple candidate keys
2. Composite candidate keys
3. Candidate keys that overlap Boyce-Codd normal form states that: Every functional
dependency should be based on a candidate key for the table.
The rule states that, once all the functional dependencies in a table are listed, all columns can be
dependent only on a candidate key of the table. In other words, in a functional dependency, the
left hand side of the functional dependency should be a candidate key. If it is not, the table
should be decomposed placing these functional dependencies along with a copy of their
determinant in a new table.
If A B is a functional dependency, and if B is not functionally dependent upon any subset of A,
then A is said to be the determinant of B.
This definition says that a determinant is a column on which some of the columns are fully
functional dependent.

BCNF – Addressing Overlapping Candidate Keys

Figure 8.3: Overlapping Candidate Keys
Composite Composite

C1 C2 C3 C4 C5

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