Re: teaching relational basics to people, questions

From: Jan Hidders <>
Date: Fri, 18 Dec 2009 00:23:54 -0800 (PST)
Message-ID: <>

On 16 nov, 20:42, Sampo Syreeni <> wrote:
> Right now it is to be expected that I will be spreading the good
> relational word among my peers, in the near future. That is an
> opportunity one doesn't want to fuck up; many enough have gone down
> that road already. So I've been going over, and over, and over the
> basics. Don't want them to be able to catch me off guard with the
> minutiae, after all...
> So now I bump into my first real surprise, and the chills immediately

> go down my spine. That's Date et al.'s answer regarding the
> implications between 6NF and DK/NF, at
> . In there they flat out state that DK/NF doesn't imply 6NF.
> So, my first question is, can this really be true? I mean, this seems
> highly suspect to me: since 6NF is a normal form like any other and is
> as such defined by the constraints it upholds by design, and on the
> other hand DK/NF is by definition a normal form where any constraint
> whatsoever follows from the domain and key ones, shouldn't it be self-
> evident that DK/NF logically implies 6NF, and in fact any other form?

Can I ask whether your question has been answered yet? I'm a bit puzzled by it because this is basically a mathematical theorem and as such the answer to it lies in understanding the math. But in your additional text you seem to question more the philosophical / intuitive foundations of these notions. Is that correct? And what is exactly your problem with that? FWIW I'd certainly agree that the justification of 6NF is suspect and weak, maybe even based on misunderstanding the relational model, and it is certainly not widely accepted.

Please be brief. ;-)

  • Jan Hidders
Received on Fri Dec 18 2009 - 09:23:54 CET

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