Re: object algebra
Date: Sat, 28 Feb 2004 23:38:55 GMT
Message-ID: <jE90c.81390$4o.104689_at_attbi_s52>
"Drago Ganic" <drago.ganic_at_in2.hr> wrote in message news:c1qvlo$agh$1_at_sunce.iskon.hr...
>
> "Neo" <neo55592_at_hotmail.com> wrote in message
> news:4b45d3ad.0402242201.72ab2c26_at_posting.google.com...
> >
> > 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 !!
Actually, I don't think it's a good question. The only relevant question, from a data management perspective, is whether "unknown" is a member of the set {red, green, blue, unknown}.
The answer to this question is yes.
> Domain should be from the problem space (semantics).
Yes.
You say:
> ... there are no ... [unknown] eye colors in the world.
and you also say:
> There are just "people" (tuples) ... who have eyes but we
> don't know the color of them.
I have a hard time reconciling the two statements.
> So I think we have to leave the domain intact.
The domain is whatever the modeller picks. There's no such thing as "intactness" for models.
Marshall Received on Sun Feb 29 2004 - 00:38:55 CET