Page 148 - DCAP405_SOFTWARE_ENGINEERING

Unit 9: System Engineering

much about modeling and simulation from reading books and talking with other people. Skill Notes
and talent in developing models and performing simulations is only developed through the
building of models and simulating them. It’s very much a learning process as you go. From the
interaction of the developer and the models emerges an understanding of what makes sense and
what doesn’t.
We repeatedly amazed at the ability of my models to point out my own ignorance. Through the
activity of developing the model and then simulating it, the simulation says, “Based on your
model and your set of assumptions, reality is absurd!” Often times the model is grossly incorrect,
and other times the model produces great leaps in my understanding of how things actually
work, and, quite often contrary to common sense. It is an amazingly wonderful journey my
models and I are undertaking.

Detail complexity is associated with systems which have many component parts. Dynamic
complexity is associated with systems which have cause and effect separated by time and or
space. The understanding is that it is dynamic complexity that we have great difficulty dealing
with because we are unable to readily see the connections between the parts of the system and
their interactions. One of the great values of simulation is its ability to effect a time and space
compression on the system, essentially allowing one to perceive, in a matter of minutes,
interactions that would normally unfold over very lengthy time periods. This is probably best
demonstrated by an example. The following example is an elaboration of one of the introductory
models in the I think documentation from isee Systems.

Example: Consider a consulting company which has 120 employees. These 120 employees
are composed of 60 rookies and 60 professionals. The company wishes to maintain the total
number of employees at 120 so it hires a new rookie for each professional who quits. Rookies
don’t quit! Professionals quit at a rate of 10 per month and it takes 6 months to develop a
professional from a rookie. Additionally, the company bills out rookies at $10k/month and
professionals at $15k/month. All 120 employees are fully applied (I know it’s a pipe dream).
A think model for this system might look like the following:

Figure 9.1: A Think Model

If you run this model you find it exists in essentially a steady state, and is about as exciting as
watching paint dry!

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