Abstract for: Model Building with Soft Variables: A Case Study on Riots

A methodology for incorporating soft variables into system dynamics models is proposed. Building on previous research, the methodology uses a systematic assessment to identify soft variables, and concepts from software engineering to implement them. Data hiding is used to separate the units and scale of a soft variable from its effect on other model elements. By encapsulating the soft variable in a module with well defined inputs and outputs, it can be used from knowledge of its parameters alone, and not its internal construction, that is it is referentially transparent. The methodology is applied to an existing population model on riot growth, extending it to include soft variables whose scales are limited. The effects of the different soft variables on the populations are combined together using cognitive algebra. The extended model is compared to historical data and found to give a richer explanation of the riot dynamics than the original model. The paper is exploratory and intended to inspire further research