Re: ERM Tool

On Fri, 15 Dec 2000 17:14:17 +0100, Christian Wandrei wrote:
>Try ER Diagrammer of KeepTool. You can download a free 30 days trial version
>from
>www.keeptool.com or www.keeptool.de. The download is the complete product
>family of KeepTool 4 (Hora, ER Diagrammer and PL / SQL Debugger).

Question: if you have a bottle with water and put a label "milk" at the bottle, what is in the bottle? Milk or water? Naturally, water. The label doesn't change the content.

Same with KeepTool's ER Diagrammer. It just produces a graphical representation of all tables and their foreign key links. That has nothing to do with entities and relationships, the basic elements of the ER approach. The same holds true for Sybase PowerDesigner.

With PowerDesigner you'll get at the first stage a physical data model (PDM), which shows tables and reference (foreign key) links. At the second stage you'll get a conceptual data model (CDM), where tables are mapped 1:1 to entities and references 1:1 to relationships. So, CDMs are just only another notation for the PDMs.

Read Peter Chen's original article in ACM's Transactions on Database Systems, Vol. 1, No. 1, published in 1976. Then you know, what entities and relationships  really mean.

Dieter Rohlfing Received on Sun Dec 17 2000 - 16:28:39 CET