Re: Normalizing the ER model

"David Cressey" <david_at_dcressey.com> wrote in message news:KigJ9.323$0I3.37277_at_petpeeve.ziplink.net...
> I think whether one wishes to apply principles of normalization to an ER
> model or not depends on what one is using the ER model for. If one is
using
> an ER model basically as a substitute for a relational model, then
> normalization proceeds pretty much the same way as it would in a
relational
> model.
>
> But there's a different way to use ER modeling. If you use ER for
analysis
> and relational for design, then normalization becomes pretty much beside
> the point for the ER model. Why do it? And I think ER is more usefully
> used this way.
>
> There is, however, a question one can ask about each attribute in an ER
> model: does the attribute truly describe the
> entity or relation that it has been attached to, or should it be attached
to
> some different entity?
>
> The answer can be subject matter dependent. If one is analyzing a
personnel
> information system, then "Date of Birth" can be an attribute of a
> "Person". Fine. But if one is analyzing an information center for a
> birthing center, then "Date of Birth" might become an attribute of a new
> entity, a "Birth".
>
> Turning an ER model into a relational model is a relatively mechanical
> exercise. That's one of the things that's good about an ER model.
>
> Oddly enough, how normalized the resulting relational model is, after
that
> transformation, is often contingent on how well you attached each
attribute
> to the correct entity of relationship.
>
>
>
> --
> Regards,
> David Cressey
> www.dcressey.com
>
>
David, you stated what I was thinking and never said. That's why I got into this argument. An ER model is conceptual. That's why many to many are accepted. And the audience understands this. It's when ERWIN converted logical to physical that we thought that logical was the real model.

Excellent points you made.

Greg Received on Wed Dec 11 2002 - 03:04:39 CET