  Recent developments using directed acyclical graphs (i.e., influence diagrams
and Bayesian networks) for knowledge representation have lessened the problems
of using probability in knowledge-based systems (KBS). Most current research
involves the efficient propagation of new evidence, but little has been done
concerning the maintenance of domain-specific knowledge, which includes the
probabilistic information about the problem domain. By making use of
conditional independencies represented in she graphs, however, probability
assessments are required only for certain variables when the knowledge base is
updated. The purpose of this study was to investigate, for those variables
which require probability assessments, ways to reduce the amount of new
knowledge required from the expert when updating probabilistic information in a
probabilistic knowledge-based system. Three special cases (ignored outcome,
split outcome, and assumed constraint outcome) were identified under which many
of the original probabilities (those already in the knowledge-base) do not need
to be reassessed when maintenance is required.
