DB Tables which are in 3NF or 4NF but not in DKNF

Question

Are there examples of Relational tables which are in 3NF or 4NF but not in Domain Key Normal Form?

Answer 1

I have no examples, but there is 5NF and 6NF between 4NF and DKNF.

Edit: link broken, replacements:

• Summary
• Wikipedia for 4NF, 5NF and DKNF

Answer 2

Yes. Domain Key Normal Form is not an enforceable normalization step. DKNF is "If every table has a single theme, then all functional dependencies will be logical consequences of keys. All data value constraints can then be expressed as domain constraints." In other words, if every constraint on the relation is a logical consequence of the definition of keys and domains, then the relation is in DKNF.

DKNF is mistakenly referred to as Sixth Normal Form (6NF) by some in the research community, but it is technically incorrect. CJ Date covers this in detail, and this On DK/NF Normal Form article is where I first learned about DKNF and understood its properties.