The following steps provide a high-level view of the model-building process, from determining the model's goals to distributing the finished model. If you are new to model building, use this procedure as a guide for organizing your thoughts and getting started with model building.
Tip: For detailed information on most of these steps, refer to the "Guidelines for the "Writing Process" chapter in An Introduction to Systems Thinking.
Define the purpose of your model, the problem you are trying to solve, or the story you are trying to tell.
Write your purpose statement down on paper and check back during the model building process to make sure that your model addresses your initial purpose.
Determine the model boundary.
Decide what needs to be in the model, what can or should be left out, and how detailed your model needs to be. Look back to your model goals in step 1 and make sure that your plan includes the entities and features that support your goals.
Map the model.
Identify the key entities in your model. You can think of this as determining the "main chain," a sequence of stocks connected by flows that provides the "backbone" of the model. Another way to start is to identify the stock you consider to be the closest to the heart of the issue you're modeling, and then add an inflow and an outflow to that stock. You can then build on to those flows and stocks. In the end, you want to account for all the stocks, flows, and converters required to model your original goals, and then make sure all feedback loops are closed.
On the Map layer, place the key entities in your model. On the Model layer, assign equations and numerical values to the entities.
Test the model.
Run the model and look for errors, anomalous values, strange or implausible behavior, etc. Fix problems you identify, then re-run the model. Continue testing and fixing until you are satisfied that your model is running correctly.
If you will be sharing your model with others, add objects on the Interface layer to help explain your model and make it easy to interact with. You can add text to describe the model's goals or to provide user instructions, and you can add interactive objects such as buttons or other ways that users can change the model's input values. You can also add graphs and tables that make it easier to read and understand the results of the model's run.
Use tools such as isee RunTime™, isee Player™, and isee NetSim™ to publish and share your model with others.
Note: For more information about using these tools, see the isee systems web site (www.iseesystems.com)