RE: [AM] justify modeling (Why Model?)

I would suggest that you don't need directions from your living room to your
bathroom - but a map might be useful if you're going somewhere you've never
been before. I tend to find that the return on visual modeling diminishes as
you become more familiar with the territory. It becomes more valuable again
if you need to give directions to someone new to the area, or if you're
planning to change the territory significantly.

Jason Gorman
http://www.objectmonkey.com

-----Original Message-----
From: Steven Gordon [mailto:[email protected]] 
Sent: 02 February 2004 17:48
To: [email protected]
Subject: RE: [AM] justify modeling (Why Model?)

Would you agree to the assertion that the less complex the story, the sooner
that modeling the story and its implmentation hits the point of diminishing
returns?  Or do you have to model all the stories before you can start
designing and implementing any story?

-----Original Message-----
From: Scott E. Preece [mailto:[email protected]]
Sent: Monday, February 02, 2004 10:41 AM
To: [email protected]
Subject: Re: [AM] justify modeling (Why Model?)



I phrased the statement badly.  Some of the modeling goals simply aren't met
by code, so there would still be value in modeling even if code were cheaper
than modeling.  However, in practice, code isn't cheaper than modeling,
because the model is an abstraction of the code.

My own rule of thumb is that a design should involve an order of magnitude
fewer symbols than the implementation of the design (for large systems, the
architecture design should be another order of magnitude more abstract).  A
model should be at that level of abstraction, so you can do several of them
and still be cheaper than code.

From my point of view, the goal is to be able to iterate the design before
you do code, because the design is smaller and, therefore, cheaper to
change, so your iterations can be much faster.  You can do substantial
amounts of validation on the models without creating code that would have to
be changed.

This should make sense even to an agilist (and certainly to an agile
modeler) - you do those cheap, lightweight models, walk through them in
various ways to validate them against your stories (use cases), revise or
replace them, all in the course of a modeling session.  The iteration is 1-2
orders of magnitude faster.

The usual rule of diminishing returns sets in at some point - it becomes
more expensive to add more detail to the model (increasing its size and
fragility) than it would to go to code.  If you're doing things right, you
have done enough exploration and validation at that point that you can
expect to not have to rework the design too radically once it's been
written.

scott

| From: Daniel Brenner<[email protected]>
| 
| Scott E. Preece wrote:
| > In all these cases the working premise is that the model is much 
| > cheaper and quicker to produce than actual code and, therefore, 
| > allows you to produce the design (both internal design and external 
| > design) in rapid iterations.
| exaggerated: if code is cheaper then forbear from modelling? And even 
| when you did model you still have no serving code (again exaggerated:
| isnt that a waste of resources? (time and money)). Or is the gained 
| benefit worth it?


--
scott preece
motorola urbana design center (il67), 1800 s. oak st., champaign, il  61820

e-mail:	[email protected]	fax:	217-384-8550
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