System modeling with dynamic reliability block diagrams

System features like security, availability and reliability, usually summarized under the concept of dependability, recently are receiving increasing attention due to the high complexity of modern systems. This imposes that specific requirements and explicit or tighter constraints have to be satisfied. However, with particular reference to reliability, there is a lack of suitable tools to properly model, analyze and (in depth) study these aspects. To fill this gap, in this paper a new modeling tool is proposed, which extends and enhances the existing reliability block diagram (RBD) formalism: the dynamic RBD (DRBD). The DRBD permits to model the dynamic reliability behaviour of a system through the proposed dependence models, exploited to represent redundancy or load sharing policies. The flexible DRBD dependencies management is based on an articulated dynamic model composed by states and events. The capabilities, flexibility, and other features of the proposed new modeling approach are illustrated through the analysis of a complex computer system taken as example.