Current performance and reliability modeling techniques and tools are seen to be, by themselves, largely inadequate for obtaining realistic predictions of the behavior of very large scale electronics systems. Numerous authors have experienced difficulties with tractability of large scale models, and have resorted to a variety of specialized, ad hoc techniques. The focus of this project is the development of a high-level formalism (language) for the specification, composition, decomposition, and solution of large scale performance and reliability models. It is expected that this formalism for model composition will aid the modeler in assembling models of these large scale systems and in understanding the errors as well as the gain in efficiency achieved by alternative model composition structures. An automated model pipefitting system is expected to emerge.