Re: Peter Chen and Charles Bachman
From: Leandro Guimarães Faria Corsetti Dutra <leandro_at_dutra.fastmail.fm>
Date: Wed, 05 May 2004 18:36:57 -0300
Message-ID: <pan.2004.05.05.21.36.57.495468_at_dutra.fastmail.fm>
>
> 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?
>
> 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.
>
> Incomplete for what?
Date: Wed, 05 May 2004 18:36:57 -0300
Message-ID: <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.
>> 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.
>> '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.
>> 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.
-- Leandro Guimarães Faria Corsetti Dutra +55 (11) 5685 2219 Av Sgto Geraldo Santana, 1100 6/71 +55 (11) 5686 9607 04.674-000 São Paulo, SP BRASIL http://br.geocities.com./lgcdutra/Received on Wed May 05 2004 - 23:36:57 CEST