Re: Entity vs. Table

From: Alfredo Novoa <>
Date: Tue, 15 Jun 2004 16:31:43 GMT
Message-ID: <>

On Tue, 15 Jun 2004 08:24:39 -0400, "Laconic2" <> wrote:

>Instead of scorning those people who did not scrap ERD, you would do well
>to learn from them.

I don't see what I can learn from them.

>I can't speak for Alan, but to me the principal value of ERD is
>communication with the SME's.

Whan an SME is?

Small and Medium size Enterprise?

>It's what I can learn as much as what I can teach. And an ERD communicates
>more effectively in this context than an RD

I completely disagree. You can communicate a lot more precisely with a relational design because it is a lot more expressive. ERD is a toy language.

>If I contrast my own experience in building successful and useful databases
>with the scenarios Dawn outlines about subject matter experts becoming
>learning enough IT to implement what they want in Pick, the salient point
>is NOT the difference in data models. It's the difference in how the gap
>between subject matter expertise and IT expertise gets bridged.

It is a lot easier to teach The Relational Model to the subject experts, and they will be able to implement or to check what they want with a little fraction of the effort needed if they used the archaic and primitive Pick.

Pick is good only for things like a phone list.

>You need both subject matter expertise and IT expertise to build either a
>good database or a good application.

And ERD does not help for this. The IT expert will think that he understands the problem but he only understands a part.

The subject matter experts don't know ERD, but most of them already know predicate logic and set theory. I prefer to teach them The Relational Model than ERD. With ERD most rules will not be captured causing a lot of communication problems.

> In cases where the subject matter is
>easily learned, the IT expert can proceed directly to design without cross
>checking analysis. Maybe in these cases, an ERD is superfluous.

>In cases where the IT expertise is easily learned, the SME can learn what's
>needed, and implement the right thing.

In my experience it is often easier to teach The Relational Model to the subject experts than to teach it to the IT "experts".

> Maybe these cases are where Pick,
>and products like it, do their best.

No, Pick is a very limited archaic toy. Here is where The Relational Model does their best.

>In cases where neither the subject matter nor the required technology are
>easily learned, and no one knows both of them a priori, it gets
>interesting. This is where we start to play volleyball.

ERD promotes volleyball because the subject matter expert can not communicate the requirements to the IT expert and the IT expert can not know the subject matter with detail. This leads to a long and painful iterative process.

Regards Received on Tue Jun 15 2004 - 18:31:43 CEST

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