Hierarchical modeling & evaluation of phased-mission systems

This paper proposes a hierarchical & modular methodology for modeling & eva luation of phased-mission systems in which phases have constant predetermin ed duration, and where missions may evolve dynamically selecting the next p hase to be performed according to the system state. A 2-level modeling is p roposed: the higher one models the mission itself, the lower one models the various phases. A separate 'modeling & resolution of phases' and 'dependen cies among phases' are considered. This methodology is applied using an exa mple of a space application. This method is compared with previous models. The advantages of this approach are in the great flexibility, easy applicab ility, and reusability of the defined models. It permits: obtaining information on the overall behavior of the system, focusing on each single phase to detect system dependability bottlenecks. The explicit modeling of the phase changes: is a neat & easily understandable representation of the interphase dependen cies, allows a straightforward modeling of the mission-profile dynamic selection. General purpose tools available to the reliability community can easily man age the computational complexity of the analysis.