# Re: teaching relational basics to people, questions

Date: Tue, 22 Dec 2009 00:01:24 -0400
Message-ID: <4b304499\$0\$5332\$9a566e8b_at_news.aliant.net>

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 <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.
```>
>
> <http://en.wikipedia.org/wiki/Sixth_normal_form>
>
> 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.

```

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

http://tinyurl.com/y9e4vxh
```
Received on Tue Dec 22 2009 - 05:01:24 CET

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