Computer aided modeling and design of industrial systems presents great potential for facilitating the construction of industrial systems which maximize utilization of materials, minimize emissions of harmful wastes, and preserve economic feasibility. A framework for modeling industrial systems that is to form the basis of a design system is described. The model takes an industrial system to be a collection of processes each characterized by their inputs and outputs of materials, energy, finances, and labor. A key concept is that of the hierarchical input/output table for materials and energy, which is formulated to facilitate the integration of industrial processes. The output of the model acts to evaluate the economic and environmental performance of the system, thus providing a means to compare different configurations. The model has a scale-invariance property that reflects the fractal nature of systems with nested flows. Suggestions are given for a computer design system for industrial clusters, wherein algorithms are used to search process databases to generate designs which link industries together to maximize utilization and profitability.