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

From: Jon Heggland <>
Date: Wed, 29 Jun 2005 09:49:48 +0200
Message-ID: <>

In article <EThwe.132522$>, says...
> >>Another small thing is updating primary keys. If a primary key has
> >>accidentally been entered wrong and you want to fix that with an update
> >>then it is usually not possible to simply update it, and the problem
> >>gets even worse if it is also refered to by foreign keys. In an ER model
> >>this is a non-problem.
> >
> > Isn't this just hand-waving? How exactly do you "indicate" the
> > relationships?
> ?? You are asking how one indicates a relationship in the ER model?

Yes. I know how to draw lines on a paper, but how do you do it on the logical level (if there is such a thing)? But it seems you answer that further down.

> > The ER model is not formal, and it's conceptual rather
> > than logical.
> I'm speaking loosely of ER-like models here, and for these there are
> already several formalizations known. See for example the work on
OMR/NIAM is very nice indeed, but it is little more than a graphical notation for the relational model. Is it really common practice to refer to it as "ER-like"? That is doing it a great disservice, in my mind.

> Formalizing the ER model is a no-brainer and that makes it a
> data model that you can compare with the RM.

In that case, you can call the RM a formalisation of the ER model as well.

Received on Wed Jun 29 2005 - 09:49:48 CEST

Original text of this message