2.9. Domain-Key Normal Form (DKNF)
Ronald Fagin defined Domain/Key Normal Form (DKNF) in 1981 as a schema that has all of the domain constraints and functional dependencies enforced. There is not yet a general algorithm that will always generate the DKNF solution, given a set of constraints. We can, however, determine DKNF in many special cases, and it is a good guide to writing DDL in the real world.
Let’s back up a bit and look at the mathematical model under normalization. An FD has a defined system of axioms that can be used in normalization problems. These six axioms, known as Armstrong’s axioms, are given below:
Reflexive: X → X
Augmentation: If X → Y then XZ → Y
Union: If (X → Y and X → Z) then X → YZ
Decomposition: If X → Y and Z a subset ...