Dependability Modeling and Analysis in Dynamic Systems

Dependability evaluation is an important, often indispensable, step in (critical) systems design and analysis processes. The introduction of control and/or computing systems to automate processes increases the overall system complexity and therefore has an impact in terms of dependability. Moreover it is of interest to evaluate redundancy and maintenance policies. In those cases it is not possible to recur to notations as reliability block diagrams (RBD), fault trees (FT) or reliability graphs (RG) to represent the system, since the statistical independence assumption is not satisfied. Also more enhanced formalisms as dynamic FT (DFT) could result not adequate to the goal. To overcome those problems we developed a new formalism derived from RBD: the dynamic RBD (DRBD). In this paper we explain how to use the DRBD notation in system modeling and analysis, coming inside a methodology that, starting from the system structure, drives to the overall system availability evaluation following modeling and analysis phases. To do this we use an example drawn from literature consisting of a multiprocessor distributed computing system, also comparing our approach with the DFT one.