Re: Question about Date & Darwen <OR> operator

"Mikito Harakiri" <mikharakiri_nospaum_at_yahoo.com> wrote in message news:1126125994.680655.39700_at_g49g2000cwa.googlegroups.com...
> 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)

Looks OK to me if you define 11 as

(H,B) -- header/body

where H = Union of all the possible attributes B = Set of (A, T, v) tuples for all the possible attributes where v assume all the possible values from T. Not quite practical really.

and 00 as ({}, {})

>
> where
> \/ is (generalized) union
> and
> /\ is join
>
Received on Thu Sep 08 2005 - 03:20:21 CEST