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.