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Roy (and Chai Choon-Lee),

Interesting alternative.  I've been a fan of the systems dynamics models 
for years.  But, I am reminded of two things.  First, the most robust 
general finding of the systems dynamics literature is that it is the 
structure (the existence of feedback loops), not the flows or rates, that 
make a substantial difference in the behavior of the model.  This is where 
SNA can shine.  SD assumes a structure and simulates a result.  SNA can 
actually explain (predict) the structure, leading to insights into why the 
critical feedback loops exist (perhaps stochastically).  It can also lead 
more efficiently to insights about critical nodes (centrality, structural 
holes, etc.) as a function of the structure.

This, however, does not take away from your primary point: SNA more often 
than not deals with fixed stationary, not dynamic, models.  Which brings me 
to my second thought: Some networkers have combined both the structural 
orientation of SNA and the dynamic orientation of simulations.  Foremost 
among these is Kathleen Carley, in my view.  She has several large scale 
packages that are built around and calculate network concepts but also use 
agent modeling techniques to simulate dynamics.  One advantage to her work 
is that she permits the structure itself to be dynamic, depending on the 
rules that govern the formation and dissolution of network links.  I would 
recommend considering some of her packages in addition to the MIT-based SD 
software.  You can find out more about these at her CASOS website; or, 
since she produces stuff so fast I am not sure the website can keep up, 
perhaps you are better off asking her directly ([log in to unmask]).

-David



--On Thursday, July 20, 2006 9:11 AM +0100 Roy Greenhalgh 
<[log in to unmask]> wrote:

> *****  To join INSNA, visit http://www.insna.org  *****
>
> Dear Chai Choon-Lee
>
> I would recommend that, rather than pursue an SNA solution (if there is
> one), you look at System Dynamics.  This explores the dynamics of flows
> and the accumulation and dissipation of resources (or stocks as they are
> called) over time. You indicate this is what you are wanting to do.
>
> There are a number of sftware packages: Stella or IThink, Vensim, and
> Powersim are the most popular: the first two are basically the same
> product, but are aimed at the schools/education market and the commercial
> market respectively.  There are student and run-time only versions from
> publisher's web sites.
>
> THE text at present is Sterman. J, 2000,"Business Dynamics: Systems
> Thinking and Modelling for a Complex World", McGraw-Hill.  A more
> approachable text is  Maani, K. E. and Cavana, R. Y., 2003, "System
> Thinking and Modelling", Pearson Education.  Both books come with CDs
> holding models in the various s/w packages as well as run-time versions
> of the software.
>
> And I would recommend, even though it is designed for K12 schools in the
> US, the  site www.clexchange.org.  This has some superb introductory
> papers, and models showing "simulation" possibly to undergrad level.
>
> Then you can make an informed decision!
>
> Best wishes ..
>
>
> Roy Greenhalgh
>
>
>
>
>
>
>
>
>
>
>
> Quoting Chai Choon-Lee <[log in to unmask]>:
>
>> *****  To join INSNA, visit http://www.insna.org  *****
>>
>> Hello,
>>
>> I am new to SNA. I am working on an engineering project that studies the
>> interdependency among critical infrastructures, such as electricity,
>> water, hospital, telecommunication, power plants, etc. I am exploring
>> the  possibility
>> of using SNA software to simulate infrastructure interdependency.
>>
>> Infrastructure interdependency gives rise to an infrastructure
>> network. In this
>> project, apart from studying the structural characteristics of
>> infrastructure network, such as centrality etc., I am wondering if there
>> is any SNA software that can be used to simulate, for instance, the
>> material/info/energy flows between infrastructures during an
>> emergency/disaster situation?
>>
>> From my shallow reading of SNA, I get a sense that SNA deals less
>> with dynamic
>> situations where different variables change as time goes by. For
>> instance, in a
>> disaster situation, medical supplies/hospital beds/food, etc. run down
>> as the clock ticks, can we use SNA software to simulate this?
>>
>> Sorry if my questions sound silly. Thank you for your time.
>>
>> Sincerely,
>>
>> Choon-Lee Chai
>> Dept of Sociology
>> University of Saskatchewan
>>
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--------------
David Krackhardt, Professor of Organizations, editor of JoSS
Heinz School of Public Policy and Management, and
    The Tepper School of Business
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-4758
website: www.andrew.cmu.edu/~krack
    (Erdos#=2)

_____________________________________________________________________
SOCNET is a service of INSNA, the professional association for social
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