A relation is in DKNF when insertion or delete anomalies are not present in the database. Domain-Key Normal Form is the highest form of Normalization. The reason is that the insertion and updation anomalies are removed. The constraints are verified by the domain and key constraints.
A table is in Domain-Key normal form only if it is in 4NF, 3NF and other normal forms. It is based on constraints −
Domain Constraint
Values of an attribute had some set of values, for example, EmployeeID should be four digits long −
| EmpID | EmpName | EmpAge |
| 0921 | Tom | 33 |
| 0922 | Jack | 31 |
Key Constraint
An attribute or its combination is a candidate key
General Constraint
Predicate on the set of all relations.
Every constraint should be a logical sequence of the domain constraints and key constraints applied to the relation. The practical utility of DKNF is less.