Re: object algebra

Bob,
Red, Green and Blue are colors."Not Applicable", "Unknown" are not. That is semantics for me .. that is something a painter or physics will understand.

I can >>mix<< Red and Green to get another color. If I mix Red and Unknown I get Unknown... That's the same problem we have now with 3VL (we would not have it with boolean algebra, but we would with "mixing" algebra, time algebra etc.)

"Unknown" should not be part of the Domain. It's part of some tuple in some relation where we don't know the color. In millions of other relations we would now. Why poisen the domain ??!

I do agree that we can model relations so that all attributs are "not null" and work with 2VL. That is one solution (i don't think it's a practical one, because we get far to many relations in our data model).

drago

"Bob Badour" <bbadour_at_golden.net> wrote in message news:UrmdnTJ4H-BildzdRVn-jw_at_golden.net...
> "Drago Ganic" <drago.ganic_at_in2.hr> wrote in message
> news:c1qvlo$agh$1_at_sunce.iskon.hr...
> >
> > "Neo" <neo55592_at_hotmail.com> wrote in message
> > news:4b45d3ad.0402242201.72ab2c26_at_posting.google.com...
> > > > If Mary has no eyes, then the definition of a person as having eyes
is
> > > > flawed.
> > >
> > > Are you saying the following set is valid or allowed in RDM?
> > > Color = {Red, green, blue, "Not Applicable", "Unknown"}
> > >
> > > Is "Not Applicable" a color?
> >
> > This question is really a good one and was not answered well !!
> >
> > Domain should be from the problem space (semantics).

>