19. A computer system comprising: a) a rule-based expert system that comprises a set of rules for evaluating the operation of a process unit in an industrial plant; b) a model-based expert system that comprises a statistical mathematical model for evaluating the operation of the process unit; wherein the computer system is programmed to perform steps comprising: receiving data on the operating conditions of the process unit; applying the model-based expert system to evaluate the operation of the process unit using 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; and 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.
19. A computer system comprising: a) a rule-based expert system that comprises a set of rules for evaluating the operation of a process unit in an industrial plant; b) a model-based expert system that comprises a statistical mathematical model for evaluating the operation of the process unit; wherein the computer system is programmed to perform steps comprising: receiving data on the operating conditions of the process unit; applying the model-based expert system to evaluate the operation of the process unit using 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; and 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. 24. The computer system of claim 19 , wherein the result from the model-based expert system is a statistical analysis result on the operation of the process unit, and wherein the rule-based expert system evaluates the statistical analysis result calculated by the model-based expert system.