SD vs System Design Engineering

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Joel Rahn
Junior Member
Posts: 15
Joined: Fri Mar 29, 2002 3:39 am

SD vs System Design Engineering

Post by Joel Rahn »

At a presentation of the SD approach to resource management (human,
equipment, financial resources), someone asked how SD compares with
System Design Engineering. Any enlightenment from this list would be
welcome. Thanks

Joel Rahn
jrahn@sympatico.ca
Alan Graham
Member
Posts: 27
Joined: Fri Mar 29, 2002 3:39 am

SD vs System Design Engineering

Post by Alan Graham »

Re Joel's audience question on System Dynamics compared to System Design
Engineering:

The purpose of System Dynamics (SD) is enabling a correct choice of policy
or strategy in a complex setting; the purpose of System Design Engineering,
or equally commonly, just Systems Engineering (SE) is roughing out a
workable architecture and overall design for a complex device (or physical
system, or even man-machine system). For example, any air traffic control
system would have SE early in the design process.

Similarities

They both tend to use models at a higher level of aggregation, and
deliberately scope the system boundaries widely. Both are likely to start
out conceptual and end up mathematical (the ""phased approach""), and indeed
sometimes both have well-articulated modeling processes.

Differences

Different purposes create many differences. SD tends to be doing just one
model at a time, and always the continuous time, lumped parameter form we
know and love. SE may well use many models, each in a different form and
drawing on different disciplines for different parts of the system to be
designed. In terms of who does it and what they know, in SE technical
engineering knowledge is the main focus, and knowledge of the client
situation is an input to the process. In SD, the modeler is expected to be
extremely familiar with all the moving pieces in the client's world. That's
because a major task of the SD modeler is to represent that world. The SE
modeler/engineer's task is to only to design something that will work as
specified within that world.

Hope this is helpful. SD vs SE is one of those questions like SD vs
Dynamical Systems where general comparison is useful to a point, just to
know what goes on in other fields and perhaps extract isolated learning
points as part of some other endeavor. (For example, for those studying the
processes of model-building, a look at how SE is taught might be useful.
Just the ""phase gate"" process is a useful allusion.) But this isn't the
right forum for deep inquiries into SE. There are too many textbooks out
there for us to duplicate the content here.

cheers,

alan

Alan K. Graham, Ph.D.
Decision Science Practice
PA Consulting Group
Alan.Graham@PAConsulting.com
One Memorial Drive, Cambridge, Mass. 02142 USA
Magdy Helal
Junior Member
Posts: 7
Joined: Fri Mar 29, 2002 3:39 am

SD vs System Design Engineering

Post by Magdy Helal »

Someone asked how SD compares with System Design Engineering

Here is what I think, being expressed without cautions...

The difference is explicit. First imagine what does a decision maker do
when he sits to look at data and then makes the decision. What do you
think he does? ... The answer is: he runs his mental model of his
process or system and gets the results, analyze them and then makes the
decision. In other words, he has a simulation model in his mind and he
just uses it.

System design engineering (not much different from the other big
concepts of TQM, 6-sigma, balanced scorecards, and all these amazing
concepts) is just a framework made of recommendations and guidelines ...
casual, qualitative, and subject to all forms of human subjectivity.

System dynamics is the materialization of the mental models. So a
decision make does not need to rely on his busy exhausted mind to run a
simulation and decide. The SD model will help. It provides a robust
tool, reliable support, quantitative guidance and protection against
subjectivity.

I believe that SD can provide what all those management fads are
missing. Besides, SD helps them to be reliably comprehensive. It does
not have to replace them. But it makes them work better.

Do we need to ask about how SD compares to other approaches ? ... No.
Instead, we need to think how can we use SD to make those approaches
work as they should.

Regards

Magdy Helal
Industrial Engi & Management Systems Dept
University of Central Florida
4000 Central Florida Blvd
Orlando, Florida 32816
e-mail:
mhelal@mail.ucf.edu
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