Re: E-R Diagrams from the database

From: Dieter Rohlfing <320003300523_at_t-online.de>
Date: Sat, 4 Dec 1999 17:53:51 +0100
Message-ID: <vugb28.6a1.ln@320003300523-0001.dialin.t-online.de>

On Fri, 03 Dec 1999 14:47:37 +0530, Anurag Minocha <anurag_at_synergy-infotech.com> wrote:

>I have a schema with different tables and their relationships defined.
>Is there any toll with which i can generate E-R diagrams from an
>existing system.

You won't get a >>real<< ER diagram from reverse engineering of table descriptions. What you will get is a graphical representation of the foreign key referencing of all those tables, nothing less, but nothing more.

What you will miss is: which table is the implementation of an entity, and which table is the implementation of a relationship.

A relationship in the meaning of the entity relationship approach is not identical with a foreign definition in a RDBMS. Specially - like an entity - a relationship can have attributes, too. Furthermore, a relationship can be defined between as many entities as you like. In the entity relationship approach there is no limitation to just two entities.

Regarding these facts the most common ER design tools are just poor implementations of Peter Chen's ER approach.

Dieter Rohlfing Received on Sat Dec 04 1999 - 10:53:51 CST