Re: Question about Date & Darwen <OR> operator

From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 03 Sep 2005 00:07:19 GMT
Message-ID: <XO5Se.357803$5V4.153773@pd7tw3no>

Marshall Spight wrote:
> 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
>

you're right; the '2 b' tuple shouldn't be there.

thanks,
paul c Received on Fri Sep 02 2005 - 19:07:19 CDT