A systematic approach to modeling and assessing gracefully degrading systems, exploiting the formalism offered by Petri nets, is provided. 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 analytically by means of a class of Petri nets to obtain interesting performability parameters either at steady state or when the system is time-varying. A number of real cases are examined and the results obtained are described.
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