This paper describes our experience in developing a software system for use in the environmental modeling community. The primary user of this software is intended to be a scientist or regulator working in the area of air quality management and pollution control strategies. The main objective of GEMS is to support the end user in performing various types of analysis requiring the processing of large amounts of data and the interaction between several high-performance computing platforms. The work described here provides the basis for an application-specific framework to support this and similar applications, including other areas of environmental modeling, chemical process control, earthquake modeling, and weather prediction. We developed our system by drawing on our experience with the object-oriented development paradigm and by using the concept of rapid prototyping. We describe the initial results of our development activities, talk about our successes, and about some of the problem...