Re: teaching relational basics to people, questions

From: Bob Badour <>
Date: Tue, 22 Dec 2009 00:01:24 -0400
Message-ID: <4b304499$0$5332$>

Jan Hidders wrote:

> On 21 dec, 23:07, r..._at_raampje.lan (Reinier Post) wrote:

>>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.
> Wikipedia is your friend:
> <>
> Whether you can call it a normal form or not is of course largely a
> matter of definition, but it clearly is different from the other ones.
> It does for example not remove redundancy or update anomalies, which
> was pretty much the whole point of the other normal forms.

1st normal form through 5th normal form involve lossless decomposition by project. Fagin proved 5th normal form is necessary and sufficient to avoid the update anomalies avoidable by lossless decomposition by project.

It has long been noted that one could create other normal forms using different operations. e.g. lossless decomposition by restrict. However, to my knowledge, nobody has done so or found a reason to.

If I am not mistaken, 6th normal form does involve lossless decomposition by project, which puts it into the same class of normal forms as 1st normal form through 5th normal form; even if the reasons for choosing 6th normal form do not involve avoiding update anomalies.

Of course, everything is a matter of definition.

is there something in it for them, like maybe bailouts, if they can 
panic us into doing something politically to cover them?

November 19, 2007 - John S Bolton
Received on Tue Dec 22 2009 - 05:01:24 CET

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