Re: View challenge

J M Davitt wrote:
...
> [Paul, you're killing me: the complement of nothing,
> indeed.]
>
> Here's the rub: there is nothing holding all values of
> "the specified range." His question described an
> instant and a period which are to be used to generate
> some intervals which are then matched to some others.
> ...

Not trying to kill anybody, JM, but a domain must define all the values, no matter what goes on in SQL.

In the D&D/TTM Algebra (and others, I presume), <NOT> RELATION {N,Integer} (or somesuch, pardon my likely syntax errors) would materialize all possible values of N. If there were already a relvar X that weren't necessarily empty, containing some values of N, "X <OR> <NOT> X" would do the same. Similarly for a relation with multiple attributes. So, I'd think the like is theoretically possible with domains of dates or times. (Type theory might help but I can't comment about that.)

D&D advocate not implementing <NOT> and <OR> - as far as I know, they reserve <NOT> merely as a way to define DELETE, and <OR> for INSERT, but I don't see any logical or practical reason why a dbms couldn't allow certain expressions of that sort, say if JOIN (<AND> in TTM) were involved in such an expression.

p Received on Sun Aug 13 2006 - 16:01:22 CEST