# Re: teaching relational basics to people, questions

Date: 21 Dec 2009 22:07:31 GMT

Message-ID: <4b2ff1a3$0$2178$703f8584_at_news.kpn.nl>

>On 16 nov, 20:42, Sampo Syreeni <de..._at_iki.fi> 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,
**>athttp://www.dbdebunk.com/page/page/621935.htm
**>> . 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.

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