Rapid changes in today's environment emphasize the need for models and
meth- ods capable of dealing with the uncertainty inherent in virtually
all systems re- lated to economics, meteorology, demography, ecology,
etc. Systems involving interactions between man, nature and technology
are subject to disturbances which may be unlike anything which has been
experienced in the past. In the technological revolution increases
uncertainty-as each new stage particular, perturbs existing knowledge of
structures, limitations and constraints. At the same time, many systems
are often too complex to allow for precise measure- ment of the
parameters or the state of the system. Uncertainty, nonstationarity,
disequilibrium are pervasivE' characteristics of most modern systems. In
order to manage such situations (or to survive in such an environment)
we must develop systems which can facilitate oar response to uncertainty
and changing conditions. In our individual behavior we often follow
guidelines that are conditioned by the need to be prepared for all
(likely) eventualities: insur- ance, wearing seat-belts, savings versus
investments, annual medical check.ups, even keeping an umbrella at the
office, etc. One can identify two major types of mechanisms: the short
term adaptive adjustments (defensive driving, mar- keting, inventory
control, etc.) that are made after making some observations of the
system's parameters, and the long term anticipative actions (engineer-
ing design, policy setting, allocation of resources, investment
strategies, etc.).