  Robustness as a system property describes the degree to which a system is
able to function correctly in the presence of disturbances, i.e., unforeseen or
erroneous inputs. In this paper, we introduce a notion of robustness termed
input-output dynamical stability for cyber-physical systems (CPS) which merges
existing notions of robustness for continuous systems and discrete systems. The
notion captures two intuitive aims of robustness: bounded disturbances have
bounded effects and the consequences of a sporadic disturbance disappear over
time. We present a design methodology for robust CPS which is based on an
abstraction and refinement process. We suggest several novel notions of
simulation relations to ensure the soundness of the approach. In addition, we
show how such simulation relations can be constructed compositionally. The
different concepts and results are illustrated throughout the paper with
examples.
