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]

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