Re: Peter Chen and Charles Bachman

"Leandro Guimarães Faria Corsetti Dutra" <leandro_at_dutra.fastmail.fm> wrote in message news:pan.2004.05.05.21.36.57.495468_at_dutra.fastmail.fm...
> Em Wed, 05 May 2004 17:02:01 -0400, Laconic2 escreveu:
>
> > Data analysis is much more pervasive than database design. Data can be
> > tied back to a conceptual model regardless of whether it is in one
> > database or another, or even different kinds of databases, whether
it's
> > in exchange in the form of XML, CSV, of the responses to SQL SELECT,
> > or in forms or reports or wherever.
>
> Useless talk, since none of these gives you a data model as
> the RM does.

If models are metaphors, can't a diagram provide such a metaphor? Sure some metaphors correspond to more components of what they are modeling than others, but that doesn't mean that a metaphor that is useful is not a model. It might make sense to use one metaphor when doing data analysis and another when doing database design, might it not?

>
> >> An ERD is a diagram. A draft. For presentation. Nothing more.
> >
> > And ERD is a diagram that represents an ER model. The ER model can be
> > more than the diagram.
> > But even if it's only the diagram, so what?
>
> It is not a model. It is a draft.
A draft of a model? If I say that "trees are like people" then you can tell me that there is no good mapping from the consciousness of a person to something in a tree. Does that mean that my metaphor is a draft of a metaphor? NO.

>
> >> 'Common key' is referential integrity, not 'relationships'.
> >
> > The use of foreign keys to represent relationships is one way to
represent
> > relationships. There are other ways. For example, in CODASYL, you
> > define a set that defines a relationship between the set owner and the
set
> > members. Referential integrity is merely a mechanism for keeping foreign
> > keys from getting orphaned.
>
> Hey, go back to your textbooks. Relationships aren't defined in the RM.

Well, the definition is often there, but it is incorrectly mapped to the word "relation" instead. It is a relationship (in mathematics) that is unordered, as someone else recently pointed out in the glossary discussions.

>
> >> So it is not a logical model. At most a conceptual one, and incomplete
> >> at that.
> >
> > Incomplete for what?
>
> For representing even the most basic constraints.

Yes, you are correct that there is no map from the consciousness of a person to something in a tree in my metaphor. Cheers! --dawn Received on Thu May 06 2004 - 00:29:50 CEST