The paper provides a systematic approach to mod- eling and assessing gracefully degrading systems, exploiting the formalism offered by Petri nets. The procedure followed is based on the definition of some fundamental modules, the composition of which allows a complete model of the system to be obtained. The model can then be solved by computer simulation or analyt- Ically by means of a class of Petri nets to obtain interesting Performability parameters either at steady state and at varying Times. The paper examines a number of real cases and describes The results obtained.
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