Re: Ecological modeling issues

[glen e. p. ropella]

Thanks for posting this, Steve!  I've been having a number of
conversations about moving CAS from a research context into
an applications context.  The overwhelming problem for the 
engineer who wants to actually use CAS (btw, I'm using
"engineer" in a very broad sense) lies with the difference
between what i think you mean by "mechanistic" vs. "empirical".
The way I characterize it is different, though.  To a large
extent, it's *both* a problem with causality (forward and 
inverse mapping between genotype/phenotype, structure/behavior,
or lexicographic/semantic) and observability (how we come
to know what the model/system is doing).  This bears quite
heavily on the comment about observing things at the system
level and on the Swarm thrust of
software-as-human/human-as-software.

Systems engineers tackle this with the rich body of experience
in verification and validation.  Often, however, that's a bit
undisciplined.  So, as far as complicated simulations are
concerned, though, systems engineering doesn't go far enough.

In any case,  I think we should be working, not on protocols
for documenting models, as such, but establishing what it
means to completely and consistently document a model.
I say this because models are wildly divergent for different
disciplines, with different goals, mechanisms, and such.

The charter for the protocols would then be to satisfy
the established criteria.  The way SwarmCorp is addressing
this is to implement several Swarm-based simulation 
systems (through contracts) and from those, abstract a 
set of criteria from those implementations.  The hope is
that the thing we abstract will then apply to more than 
just the instances we abstracted from.  But, we're a ways
away from that, yet.  I think this approach is the only one
that's going to work.  Prescriptive specification of these 
criteria will probably fail in the same way that UML is 
failing. (I know, I shouldn't say that because I don't have
the energy to justify my statment that uml is failing. [grin]
But, it's never stopped me in the past.)  The ad-hoc approach
is the only one that has worked in the past; but, it's clearly
not up to the task (as you and Dr. Grimm point out) because
people confuse model encodings with models.  The bottom-up
approach (with good doses of the other two, of course) is 
our last best hope.

Anyway, thanks for posting that, Steve.

glen


At 08:16 AM 4/21/99 -0700, you wrote:
>In my presentation to SwarmFest I briefly cited a new paper by Dr.
>Volker Grimm; it was one of several interesting papers in the February
>issue of Ecological Modelling (vol. 115, pages 110- ), which was
>dedicated to individual-based modeling in ecology. Dr. Grimm's paper
>points out problems with how IBMs have been built and used, many of them
>software-related (I am trying to convert him into a Swarmist). 
>
>He also makes the interesting point that ecologists miss a very
>important opportunity when they fail to use IBMs for comparison to
>traditional ecological models and theory. (I suspect the same point
>applies to economists and other users of agent-based models that are
>designed to depict real systems.) The Intro to this paper is posted on
>Dr. Grimm's site: http://www.oesa.ufz.de/volker/volker.htm
>
>A second paper in this issue (Lorek, H. and M. Sonnenschein. “Modelling
>and simulation software to support individual-based ecological
>modelling.” Ecological Modelling 115: 199-216.) discusses 3 kinds of
>software: (1) library or framework systems (like Swarm and Dr. Lorek's
>ECOSIM package, which is designed specifically for ecological IBMs); (2)
>tools for specific kinds of models, which are easy to use but can only
>be modified to a limited extent; and (3) simulators for one specific
>application. Dr. Lorek was working on a package "WESP" as a type (2)
>tool and as a way to make type (3) simulators. Unfortunately, Dr. Grimm
>tells me that H. Lorek has left their research institute so the fate of
>ECOSIM and WESP are uncertain.
>
>For anyone interested in simulation of real and complex systems and
>related software issues, here are excerpts of a note from Dr. Grimm,
>after I sent him some comments on his paper (">" denotes my words).
>Please note his comments on ecology at SFI, documenting models,
>comparing IBMs to classical theory, frameworks for "bottom-up" modeling.
>
>References or interests in any of these issues are welcome! 
>If anyone out there is working on protocols for documenting models,
>please contact Dr. Grimm. 

--
glen e. p. ropella                =><=          Hail Eris!
Home: http://www.trail.com/~gepr/home.html  (505) 424-0448
Work: http://www.swarm.com                  (505) 995-0818  


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