Digest: A New Tool for Creating Insightful System Stories

System stories” are systematic verbal accounts of how key parts of a model’s structure influence important patterns of behavior in the model. System stories are how managers make sense out of model output and understand a system’s dynamics. This paper identifies three ways of thinking all of which support the creation of system stories— operational thinking, feedback loop thinking, and dynamic thinking. Dynamic thinking requires that the modeler be prepared to describe precisely what structure influences most strongly a given pattern of behavior. The paper briefly defines and describes the Pathway Participation Metric (PPM), a mathematical calculation (that can be related to eigenvalue analysis) as a useful algorithm for identifying influential structure. Next, the Digest software is presented. Digest is not a simulation language. Rather Digest accepts a text version of a simulation model from any commercial system dynamics package and performs post formulation analysis of the model. Digest is an experimental piece of software that automatically detects and then displays which feedback loops are most influential in explaining a selected pattern of behavior in a model. Output from a sample Digest run is presented and described. System Stories: Understanding How and Why Patterns of System Behavior Arise from Most Influential System Structure An important purpose of many system dynamics modeling efforts, indeed of most such modeling projects, is to help teams of non-technical managers better understand the systems which they manage and in which they live. One key task in this search for