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

If the model serves as the communications vehicle with the client,
it may survive several iterations of the code, before the point of
diminishing returns sets in.  The model may be the best vehicle to
describe to the client what is changed and why.  It also serves as
a means to communicate with a large team of persons, so that the
project manager can be assured that the team is aboard before the
solution is presented to the client.  

Pat

-----Original Message-----
From: Steven Gordon [mailto:[email protected]] 
Sent: Monday, February 02, 2004 12:48 PM
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
phone:	217-384-8589	cell: 217-433-6114	pager:
[email protected]

For more information about AM, visit the Agile Modeling Home Page
at www.agilemodeling.com

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For more information about AM, visit the Agile Modeling Home Page at www.agilemodeling.com
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