Elsewhere, we have defined unanticipated events as all unpredictable changes to the agent's problem-solving situation [Turner, 1994]. We do not necessarily mean only those things that are novel or completely unexpected, however (though we do not rule those out). Instead, we mean ``unpredictable'' in the sense that a person stepping in front of a car is unpredictable: although it is likely that, if asked, the driver would have been able to predict that at some time some person could step in front of his or her car at some place, the exact combination of time and person and place was utterly unpredictable in advance.
Unanticipated events in the context of multiple agents force us to consider
not only events that impact a single agent's problem-solving activities, but
also those that impact one or more other members of the group or the group as
a whole. This is hampered by the essentially local view that any particular
agent has of its world. Agents build their view of the world based on input
from sensors, their understanding of the effects of actions in the world,
knowledge of the way agents interact (including the overall organizational
structure and agents' roles in it), and knowledge about what other agents may
believe concerning a particular situation. Unfortunately, this local view is
inherently incomplete and uncertain.
In addition, the
agent cannot ignore the effects of its actions and changes in its beliefs on
other agents with which it cooperating. These two things, a local world view
and interdependence of agents' actions and beliefs, impact all phases of event
handling.