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

Well, yes and no.  I agree with respect to modeling a particular story.
However, I think the biggest win comes in the lightweight up-front
design stage where you're figuring out the archtiecture that ties the
pieces together. At that point you probably are thinking about all the
stories for the iteration and how they interact, probably factoring in
some knowledge of the big picture of the system, too.

scott

| From: Steven Gordon<[email protected]>
| 
| 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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