Belief Revision and Trust
  Belief revision is the process in which an agent incorporates a new piece of
information together with a pre-existing set of beliefs. When the new
information comes in the form of a report from another agent, then it is clear
that we must first determine whether or not that agent should be trusted. In
this paper, we provide a formal approach to modeling trust as a pre-processing
step before belief revision. We emphasize that trust is not simply a relation
between agents; the trust that one agent has in another is often restricted to
a particular domain of expertise. We demonstrate that this form of trust can be
captured by associating a state-partition with each agent, then relativizing
all reports to this state partition before performing belief revision. In this
manner, we incorporate only the part of a report that falls under the perceived
domain of expertise of the reporting agent. Unfortunately, state partitions
based on expertise do not allow us to compare the relative strength of trust
held with respect to different agents. To address this problem, we introduce
pseudometrics over states to represent differing degrees of trust. This allows
us to incorporate simultaneous reports from multiple agents in a way that
ensures the most trusted reports will be believed.
