Re: Question about Date & Darwen <OR> operator

Mikito Harakiri wrote:
> VC wrote:
> > What is a "cylidric set" ? Probably you meant 'cylindric set algebra'
> > rather than a "cylindric set". If so, it's unclear whether talking about
> > databases in terms of cylindric set algebra is more insightful or clarifying
> > than doing the same in terms of relations and predicates. If not, what
> > exactly do you mean by "Cylindric sets are geometric objects which are
> > invariant under projection" ?
>
> I take back my reference to cylindric sets.
>
> Let me give a very succinct lattice definition instead.
>
> A <OR> B == (A /\ 11) \/ (B /\ 11) \/ (A /\ B /\ 00)
>
> where
> \/ is (generalized) union
> and
> /\ is join

Given fundamental relation decomposition

R = (00 /\ R) \/ (11 /\ R)

it is illustrative to compare A<OR>B with A\/B:

A \/ B = (A /\ 11) \/ (B /\ 11) \/ (A /\ 00) \/ (B /\ 00) Received on Wed Sep 07 2005 - 23:07:16 CEST