Oracle FAQ Your Portal to the Oracle Knowledge Grid
HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US
 

Home -> Community -> Usenet -> comp.databases.theory -> Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

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

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Wed, 29 Jun 2005 09:49:48 +0200
Message-ID: <MPG.1d2c70f48d0be679896bc@news.ntnu.no>


In article <EThwe.132522$eO.7105566_at_phobos.telenet-ops.be>, jan.hidders_at_REMOVETHIS.pandora.be 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
> ORM/NIAM.
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.

-- 
Jon
Received on Wed Jun 29 2005 - 02:49:48 CDT

Original text of this message

HOME | ASK QUESTION | ADD INFO | SEARCH | E-MAIL US