Dependability of complex, large, dynamic systems

Today's reliability methodologies and tools need to assess increasingly large, complex systems. Moreover, in order to adequately evaluate the system dependability it is necessary to take into the right consideration system dynamics. Combinatorial techniques can be adopted in case the system's units are two-state (Boolean) and stochastically independent. Otherwise, it is requested to recur to lower level techniques and formalisms, such as: state space methods, or simulation. This paper analyzes the dependability of large, complex systems affected by dependent/dynamic behaviors. Starting from dynamic reliability block diagrams, a notation we developed by extending the reliability block diagrams, we detail how this modeling approach captures dynamic reliability behaviors. In order to demonstrate the effectiveness of such technique, we investigate some common/specific dynamic reliability/availability behaviors, providing the guidelines for their representation and evaluation.