more closed-world chatter

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 Wed May 02 2007 - 15:13:21 CDT