A domain-specific language for urban simulation variables

UrbanSim is a modeling system for simulating the development of urban regions over periods of 20-30 years. Its purpose is to help evaluate alternative proposed policies and transportation infrastructure projects by simulating the long-term impacts of the different alternatives. In the process of adapting and calibrating the system for use in a new region, planners and modelers must prepare input data, specify and estimate a set of component models, and assess the results before giving them to policy makers. All of these activities involve considerable investigation and experimentation using different model variables that describe attributes of actors, processes, and geographies of the simulated environment. In many cases, the original variables must be transformed or combined to create new variables that are more suitable for analysis; and in other cases, creating new variables on the fly may facilitate exploration of the results. In this paper we describe the design and implementation of domain-specific language for specifying these variables, with a syntax and semantics tailored to the domain. As a result of using this language, the code size for specifying variables is reduced by an order of magnitude, and user productivity is greatly increased.