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

"David Cressey" <cressey73_at_verizon.net> wrote in message news:ncR8j.287$qv1.250_at_trndny01...
>
> "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.
>

It's also wrong. Consider,

R(a*,b*,c*) where a*, b* and c* are each keys,

R is not in 6NF because it can be decomposed into

R1(a*,b*) and
R2(a*,c*)

even though R doesn't have any non-key attributes!

> 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?
>
>
Received on Sat Dec 15 2007 - 20:57:36 CST