Method and apparatus for monitoring and diagnosing sensor and interactive based process systems. The knowledge base concerning the process system per se is in the form of a list stored in memory, which list includes domain specific rules in evidence-hypothesis form. This domain dependent information is devoid of means for interconnecting the rules to perform diagnostic services. A completely domain independent set of meta-level rules is stored in memory, which, in response to sensor and/or user input, searches the knowledge base and effectively constructs a rule network through which belief is propagated, to detect and report malfunctions, to output control signals for modifying the operation of the monitored system, and to aid users by providing information relative to malfunctions which pinpoints probable causes. The domain independent rules, in addition to the meta-level rules which search the knowledge base and interconnect domain specific rules, includes procedural rules for choosing which of the meta-level rules to apply when there is a choice. The procedural inference rules are independent and distinct from the meta-level rules which manipulate the knowledge base.