Domain Key Normal Form DKNF

Domain Key Normal Form DKNF is also called 6NF.

Our relations have no constraints other than domain constraints and key constraints.

Domain constraints

Domain constraints specify the possible values of the attribute.

E.g. The only colors of hair are black and white

E.g. The CGPA of a student is between 0 and 4.

Key constraints

Key constraints specify keys of some relation.

General constraints

General constraints or any other constraints which can be

expressed by the first-order logic.

E.g. If the first digit of a bank account is 2, then the balance of

the account is greater than >=4000.

It’s logically wrong because Balance is nonprime attribute and determining the type. In this case, a transitive dependency is occurring.

Domain constraint: If Regular_Account, then the first digit of  AccountNo will be  2 and balance < 4000

 Domain constraint: If Executive_Account, then the first digit of AccountNo will be 1 and balance ³ 4000.

Solution: Separate table for  Regular_Account and Executive_Account.

Table: Regular_Account

 

Table: Executive _Account

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