Re: more closed-world chatter

> > My feeling is that INTERSECT isn't worthy of
> > much inspection, because it's not a generic
> > relational operator and it can't do anything that
> > we can't already do with generic relational
> > operators. The same goes for specialized
> > MINUS. Generalized MINUS, on the other
> > hand, is worthy of attention.
>
> Is generalized minus the same as semiminus?

I suggest semijoin as a generalized minus. The generalized Date identity is:

(A /\ B) \/ (A /\ 00) = A \ (A \ B)

where /\ is join, \/ is generalized union, and \ is antijoin.

On a related note, is anythig special about

A / (A / B)

where / is relational division? Received on Thu May 10 2007 - 18:42:32 CEST