Dependability of Modular Software in a
Multiuser Operational Environment
Effects of shared use on the dependability of modular software are
evaluated in terms of a generally defined stochastic model.
The total system in question consists of a community of n users who
share a software system with m modules.
The input aspect of the
operational environment, reflecting user demands at the module level,
is represented by a continuous-time, finite-state Markov process,
called the operational profile. The profile's construction is based on
the isolated profiles of individual users which, in the case of
heterogeneous use, are pairwise-distinct processes. Moreover, in the
presence of other users, an individual profile can differ
from its isolated version due to "slowdowns'' caused by sharing.
This multiuser profile is combined with a failure model which,
among other things,
captures "stress'' due to shared use.
of basic issues are then addressed
and resolved in terms of closed-form dependability solutions
obtained for elementary 2-user, 1-module systems.
Specifically, three measures are investigated in this manner,
insight into how dependability, as perceived
by a subject user, is affected by the profile of an interfering user.
Keywords: Dependability, model-based evaluation, modular
software, design faults.
Compressed PostScript File: