Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

In article <42a6b3ad$1_at_news.fhg.de>, savinov_at_host.com says...
> The point was what one table means by itself? Assume you
> have no records. Then you create a table, say, DEPARTMENT_01, with some
> columns or without columns. Is it a fact from you problem domain? There
> have been two opinions:
>
> 1. It is not a fact (entity). Tables are special constructs that have
> nothing to do with representing facts. They have special meaning
> completely different from that of facts and hence they have special
> mechanisms for manipulating and representing.
>
> 2. It is a fact. Tables represent some entites from the problem domain
> just like records. In this example, DEPARTMENT_01 *is* some entity,
> which is however represented by a table rather than a row in some other
> table.

I see. In the RM, a relvar is not a fact (proposition), it is a predicate. So #1 is the closest, although it is incorrect to say that they "have nothing to do with representing facts"---they have very much indeed to do with it.

However, I think I see where our disagreement lies now.

> This is precisely the point we started to discuss. This topic is much
> wider that RM or data modeling. It is very important in ontologies, in
> OO programming (is class an object) and other fiedls, and it can be
> reformulated in different terms.

Is class an object---that is the question! Our problem is that I subscribe to Date and Darwen's view that class does *not* correspond to relvar (table); class corresponds to domain/type. It seems very likely to me that you disagree, and thus we cannot agree on the implications of this.

-- 
Jon