Re: Question about Date & Darwen <OR> operator

paul c wrote:
> Mikito Harakiri wrote:
> > Marshall Spight wrote:
> >>As I understand it, the result would be:
> >>
> >>x y
> >>---
> >>1 a
> >>1 b
> >>2 a
> >>
>
> i believe the answer is not the above, rather there are 4 tuples, two
> with x=1, ie. one for each of all possible values of the y domain and
> two y=a, ie. one for each of all possible values of the x domain.

I note that the above answer *does* have two tuples with x=1, and two tuples with y=a. However if you count them up you will see that makes for three, not four.

I don't see how one could argue for the tuple (x=2, y=b) to be included,
since (x=2, y=b) doesn't satisy the condition that x=1 or y=a. Put another way, if we project the result over x, we get a value that wasn't in the x input relation, and if we project over y, we get a value that wasn't in the y input relation.

Marshall Received on Sat Sep 03 2005 - 02:02:59 CEST