Re: more closed-world chatter

Since 3 is not in the domain of item prices, I would expect a type mismatch exception. What is the difference between 'select from items where Price = 3' and 'select from items where Price = "Arm" or Price = "Leg"' in that regard?

"paul c" <toledobythesea_at_oohay.ac> wrote in message news:Bh6_h.155482$aG1.143414_at_pd7urf3no...
> If I have a domain of items consisting of the values "a" and "b" and a
> domain of item prices consisting of the values "1" and "2" and an empty
> relation {ItemID, Price} known by the relvar name "Items", I take it that
> the logical complement of "Items" has four tuples - loosely,
> <a,1>,<a,2>,<b,1>,<b,2>.
>
> If I select from Items where Price = 3, should a dbms answer with an empty
> relation or should it take exception, such as "illegal question"? If it
> doesn't take exception, then I'd guess it is supposing a complement that
> has an infinite number of tuples which couldn't be implemented on a finite
> computer.
>
> As unhappy as this makes me, I'm now thinking exceptions can't be avoided
> in practice.
>
> p
>
Received on Thu May 03 2007 - 02:05:55 CEST