Re: teaching relational basics to people, questions

From: Reinier Post <rp_at_raampje.lan>
Date: 21 Dec 2009 22:07:31 GMT
Message-ID: <4b2ff1a3$0$2178$>

Jan Hidders wrote:

>On 16 nov, 20:42, Sampo Syreeni <> wrote:
>> 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,
>> . 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

I don't think so. It's hard fo me to tell, because I just did the required math and it turns out don't have $60 to spend on the book which contains the definition of 6NF required for this discussion, but if I can get by the Google Books preview, it appears to involve some degree of interpretation of domain values (as being totally ordered). Normal normal forms don't do this.

>> 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?

Any constraint of the kind used in normal forms, perhaps. Constraints that involve interpretation of domain values aren't among those.

>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.

It's probably a mathematical theorem, once you've bought it. I believe Sampo's objection is a purely mathematical one.

Received on Mon Dec 21 2009 - 23:07:31 CET

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