Re: Newbie question about db normalization theory: redundant keys OK?

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 15 Dec 2007 10:43:04 -0400
Message-ID: <4763e7fe$0$5273$9a566e8b@news.aliant.net>

David Cressey wrote:

> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:4763dc87$0$5291$9a566e8b_at_news.aliant.net...
> [snip]
>

>>6NF:
>>R1(a*,b)
>>R2(a*,c)
>>
>>6NF has at most one non-key attribute.

>
> Thanks for the above definition. It's simple, and easily understood. I
> actually "invented" this form on my own in my head, but didn't think it was
> important enough to merit giving it a name.
>
> The interesting thing about 6NF is that the entire argument about NULLS is
> obviated by 6NF. Instead of including a null, you just omit a row. Then
> the argument switches to CWA versus OWA. The people who like to argue will
> always prevail. Sigh.
>
> Are there any INSERT, UPDATE, or DELETE anomalies in DKNF that disappear
> when one decomposes into 6NF? It has been my understanding that DKNF was
> final in the sense that no further update anomalies would surface in any
> DKNF schema.
>
> My understanding comes from my reading in this newgroup. I may have read
> somebody else's post wrong, or the other poster may have been wrong. When
> was 6NF invented or discovered?

It was invented by Lorentzos, Date & Darwen for temporal databases. In the example above, it is easier to add time intervals to the keys for R1 and R2 than for R when b and c can change independently. Received on Sat Dec 15 2007 - 08:43:04 CST