# 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.

account |
Balance | Type |

1-T4Tutorials-110 | ||

2-T4Tutorials-211 |

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.

account |
Balance |

1-T4Tutorials-110 | |

2-T4Tutorials-211 |

**Table:** Regular_Account

account |
Balance |

1-T4Tutorials-110 | |

2-T4Tutorials-211 |

**Table:** Executive _Account

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