Path: utzoo!utgpu!watserv1!watmath!att!att!linac!uwm.edu!zaphod.mps.ohio-state.edu!samsung!munnari.oz.au!metro!usage.csd.unsw.oz.au!ccadfa!ghm
From: ghm@ccadfa.adfa.oz.au (Geoff Miller)
Newsgroups: comp.databases
Subject: Re: ER versus dependency normalization methods.
Message-ID: <2095@ccadfa.adfa.oz.au>
Date: 27 Nov 90 22:37:44 GMT
References: <33445@netnews.upenn.edu>
Organization: Computer Centre, University College, UNSW, ADFA, Canberra, Australia
Lines: 40

aaron@grad2.cis.upenn.edu (Aaron Watters) writes:

[...some good common sense deleted just to save a bit of space...]

>Consider the scenario:  To design a database you first
>1.	-draw an ER-diagram of the information of interest
>2.	-by inspecting the ER-diagram derive a heap of
>	dependencies and attributes.
>3.	-toss the lot into a normalization procedure.
>4.	-if the output doesn't look like the ER-diagram at
>	step 1, go back to (2) and figure out what you
>	left out.
>Close analysis will reveal that steps 2-4 are redundant.

>Now I'm not interested in getting into some high level
>shouting match -- but could someone come up with a simple
>compelling example which demonstrates why I'm wrong about
>this?		-aaron.

Basically I don't think you are wrong -- although you may have oversimplified
a bit!  Some years ago I read De Marco's "Structured Analysis and System
Specification", and while I can't say I follow his (or anyone else's)
methodology exactly he put a lot of emphasis on *simple* diagrammatic
representations and on the use of different *levels* of detail.  While he
mostly used this for processes, the same approach can easily be applied to
ER diagrams or variants thereof.  By keeping each diagram simple they 
become much more managable and -- as you suggest -- much more directly useful.

I guess the formal methodologies may have a place in the design of very
complex systems, although I would always prefer to approach these in a less
formal way as simpler sub-systems.  However, to paraphrase Sturgeon's Law
(90% of everything is crud), "90% of computing is common sense dressed up
in jargon".  People were using normalisation and relational file structures
before Codd formalised that approach, and people were drawing pictures long
before they were formally defined as ER diagrams.  The way to approach any
of the formal methodolgies is to look at what underlies them and take what
is useful for your particular application.

Geoff Miller  (ghm@cc.adfa.oz.au)
Computer Centre, Australian Defence Force Academy