A tutorial on simulation modeling in six dimensions

Abstract

Simulation involves modeling and analysis of real-world systems. This tutorial will provide a broad overview of the modeling practice within simulation by introducing the reader to modeling choices found using six dimensions: abstraction, complexity, culture, engineering, environment, and process. Modeling can be a daunting task even for the seasoned modeling and simulation professional, and so my goal is to introduce modeling in two ways: 1) to use one specific type of model (Petri Net) as an anchor for crossdimensional discussion, and 2) to provide a follow up discussion, with additional non Petri Net examples, to clarify the extent of each dimension. For example, in the abstraction dimension, one must think about scale, refinement, and hierarchy when modeling regardless of the type of modeling language. The reader will come away with a broad framework within which to understand the possibilities of models and of modeling within the practice of simulation. INTRODUCTIONThe title of this paper is a little odd because it may sound as if I am referring to "six dimensional objects or space" as one might have in physical theories. However, the word dimension is used as a means to categorize important aspects of the modeling practice (Fishwick 1995). Models, for instance, can be abstract or they can be detailed. This observation is true regardless of the model type. Abstraction is a universal quality of objects and their behaviors. By thinking about abstraction, one is able to become a better modeler. There is also a danger of being too general. If I provide definitions for six dimensions, you may be at wits end to come away with a good sense of modeling. So, I will provide definitions for each of the dimensions, but also provide discussion grounded on one model type (a Petri net) for each dimension. Then, I'll employ various other examples for each dimension for a more thorough explanation. By moving from a standard Petri net model type to a free-form discussion, the dimensions can be better understood. Many of the references are from prior Winter Simulation Conference proceedings in the tutorial sections so that the reader can easily link to these freely available online proceedings papers. Before proceeding with the task of illustrating models, let's briefly define modeling. Modeling is the task of building a model, with a model consisting of a product containing features that emphasize certain attributes of a phenomenon. Modeling is so natural to humans that we do it routinely. A map is a model of territory-by taking a map on a journey, we can find our way around. The map serves to highlight, or surface, certain aspects of the territory. A toy train is a scaled down model of a train. Such scale models are often specified by their numerical scale: 1:10 or 1:100 for instance, with a 1:10 model being 1/10 th the size of the real train. Figure 1 shows a scale model of a favorite destination of mine, Bourton on the Water, which is a small village in Gloucestershire, England. You visit Bourton, park your car, and then l...