Re: 4NF is Where It Is At! [WAS Re: 1:1 relationships]
Date: Wed, 14 Feb 2001 16:27:41 GMT
Message-ID: <3a8aad8c.2075741_at_news.which.net>
On 14 Feb 2001 10:13:49 GMT, hidders_at_REMOVE.THIS.win.tue.nl (Jan
Hidders) wrote:
>What often works is looking at what happens if you denormalize.
Thank you for the example, Jan. I have now worked through this and
Date's Chapter 11 and the light has dawned about MVDs.
I think my problem is summed up by a note which Date made:
I have always done this under the impression that it was part of _1NF_
>Suppose, for instance, you have the following normalized tables:
>
> Is_member_of(student, class) key: {student}
> Follows(class, course) key: {class, course}
>
> . . . snip . . .
>
> So, I hope this already helps you understand
>MVDs a little better and also when and why they should be split out of
>the table.
>
>--
> Jan Hidders
"In practice it is usual - by separating independent repeating
groups - to eliminate such MVDs _before_ applying [the
normalisation rules] . . ."
Thank you very much for your help.
Regards
Peter Franklin Received on Wed Feb 14 2001 - 17:27:41 CET