Re: 4NF is Where It Is At! [WAS Re: 1:1 relationships]

In article <96gd0d$7qs$1_at_news.tue.nl>, Jan Hidders says...
>
>Second, I would like to ask Vadim to post inside a thread if it is
>relevant and not start a new thread with the same subject line.
>

I sincerely apologyse, but now that deja is gone, I have do some testing what other web services really work...
>
>I think the 'or' should be an 'and'. Otherwise this is not a sufficient
>condition. Note that your condition is equivalent with saying that
>
> ~(R[CT]) JN R[X] <= ~R or ~(R[CX]) JN R[T]) <= ~R
>

'or' is always a union, isn't it?

Besides, there is only one 0-cylinder enclosing a 0-point <Math, Green, Opt> : <Math, Green, Opt> + <Math, Brown, Opt>

>where ~ is 'complement' and <= is 'subset or equal'. But in your
>'reconstruction' you are already showing that
>
> ~R = (~R[CT] JN R[X]) + (~R[CX] JN R[T])
>
>where + is the set union. Why you think this is simpeler than just
>saying that R = R[CT] JN R[CX] is not really clear te me. :-)

I write mine rather as

~R = (~R[CT] CP X) + (~R[CX] CP T)

without joins. Received on Thu Feb 15 2001 - 19:38:55 CET