1. An apparatus for detecting problems in a system which generates a plurality of symptoms, said apparatus comprising: a) a storage device storing a Bayesian network model representing a domain of knowledge about the system wherein each node of said model represents one of the state of the system, the state of a component of the system, and a symptom, and each node is associated with a conditional probability matrix which specifies the relationship of the node to one of probabilistic dependents and probabilistic antecedents in the model; b) monitoring means for monitoring a plurality of symptom data values; c) means for instantiating symptom data values in said Bayesian network model; d) means for automatically updating appropriate probability matrices on the basis of new knowledge obtained by said monitoring means about the probable association of symptoms with problems and thereby changing said Bayesian network model to better represent said domain of knowledge as new knowledge accumulates; and e) means for using said updated Bayesian network model to detect problems in the system.