The WinASSIST program uses a rule-oriented language to automatically generate input files for the SURE/WinSURE program. The user describes the failure behavior and recovery behavior of a fault-tolerant computer system in an abstract language. The WinASSIST program then automatically generates a corresponding semi-Markov model. The abstract language allows efficient description of large, complex systems. A one-page WinASSIST-language description may result in a semi-Markov model with thousands of states and transitions. The WinASSIST program also provides model-reduction techniques to facilitate efficient modeling of large systems.