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Re: Latest version of glossary

From: JOG <jog_at_cs.nott.ac.uk>
Date: 25 Feb 2006 07:35:25 -0800
Message-ID: <1140881725.910649.205530@p10g2000cwp.googlegroups.com>


David Cressey wrote:
> I read exactly the same paper you did, and I had a very different response.
> I found the lack of formality in the ER to be refreshing, rather than awful.
>

Hi David. I didn't think the paper was awful - just Chen's definition of an entity. Anything with apologetic quotes in it sets of alarm bells. The paper as a whole is good, and has clearly had significant impact on the field which is a sign of its strength - it is now rather old and although academically it has been superceded by Nijssen and Halpin (NIAM/ORM) we are still discussing it over 25 years later.

> Maybe that's because it blends well with my experience at the data analysis
> stage of projects.
>
> At that stage, most people have a poorly formed notion of what they are
> talking about. Even the subject matter expert is at a loss to understand
> why data has to be discussed in such formal detail, when he's got the stuff
> in his mind? The technical people in the room almost always understimate
> the complexity of the necessary model to make the analysis comprehensive
> enough.

Indeed - flexibility, flexibility, flexibility. I am starting to appreciate just how important it is in practical situations, and that this is an area that should be a primary consideration for a data model.

>
> An analysis that doesn't dig deep enough results in a model that has to be
> extended too many times during the project, and that in turn has a
> devastating effect on "bang for the buck".
>
> The fact that "entity" is so poorly defined is related to the way we think.
> All of us tend to analyze the universe of discourse into parts. Various
> religions, at one time or another, have commented on the essential unity and
> indivisibility of the universe. But they don't have to build databases. We
> do.
>
> But the analysis of the universe of discourse into entities is SUBJECTIVE
> regardless of how much effort we take to make it seem objective.

True, but we are just talking about a definition here, not the impact of formalising entities into actual mechanism. However I broadly agree, and any definition of an entity, ought emphasise that it is a subjective not objective item.

> A less formal approach at the analysis stage allows for more fuzzy thinking
> at that stage. IMO, that's a good thing. There will be time to tighten up
> later, when we convert the ER model to a relational model (or a codasyl
> model or a hierachical model, or an MV model or an object model).
> Sloppiness in the analysis will be uncovered and resolved at that point.
> And that point is still before coding has begun.

I was suprised when I read Chen's introduction however that he did not initially view ER as something to be translated from, but rather a model of the same order as codasyl/MV/RM, standing in direct competition with them. It is interesting to see how the position of ER has evolved to a design tool utilised prior to implementation into a different model.

>
> I have a great example from a project long ago, but I'll save it for
> another topic.

look forward to hearing about it.

All best, Jim. Received on Sat Feb 25 2006 - 09:35:25 CST

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