Re: more closed-world chatter

On May 11, 4:03 am, Jon Heggland <jon.heggl..._at_idi.ntnu.no> wrote:
> Marshall wrote:
> > If we are joining X with DUM, then there are necessarily no
> > attributes in common, so we would not expect to perturb
> > the attribute types from X.
>
> So you won't consider each type of the result to be additionally
> constrained by "and false", thus leading to the bottom type?

Oh, um, uh, yeah, that would work.

I don't have the clarity on this issue yet that I need to. I'm used to thinking about traditional type systems but I'm trying to transition to thinking about more general constraint systems, and sometimes I confuse myself.

> >> Is generalized minus the same as semiminus?
>
> > As Vadim mentioned, it is more traditionally called
> > antijoin. (And has he has also mentioned, it's an
> > unfortunate name since it's the inverse not of
> > join but of generalized union.)
>
> That isn't obvious to me, but then I have always had trouble
> understanding those inverses you and Vadim are talking about.

I'm trying to come up with a better explanation of these as well.

Marshall Received on Fri May 11 2007 - 09:30:27 CDT