10. The method of claim 1 , wherein the step of applying the rule-based expert system comprises evaluating the set of rules according to a rule evaluation schedule, and wherein the method further comprises the step of making a rule evaluation schedule, which comprises the steps of: adding to the rule evaluation schedule, a first set of rules whose conditions do not depend on other rules; and adding to the rule evaluation schedule, a second set of rules that are not already in the schedule whose conditions include dependencies on rules in the first set of rules but do not depend on any other rules.
1. A method for operating an industrial plant, comprising: having a rule-based expert system that comprises a set of rules for evaluating the operation of a process unit in the industrial plant; having a model-based expert system that comprises a statistical mathematical model for evaluating the operation of the process unit in the industrial plant; applying the model-based expert system to evaluate the operation of the process unit using statistical data on the operating conditions of the process unit; obtaining a statistical analysis result from the model-based expert system; applying the rule-based expert system to identify a possible abnormality in the operation of the process unit using: (a) data on the operating conditions of the process unit, and (b) the result from the model-based expert system; sending a first message from the rule-based expert system regarding an abnormality to an operator interface; suppressing a second message from the model-based expert system, wherein the suppressed message relates to the abnormality and is redundant to the first message; and adjusting the operation of the process unit based on the message relating to the abnormality.