Abstract: This invention provides a computer operated process control system and method for controlling an external process control system using a combined rule-based expert system in combination with a procedural control system. The computer operated process control system includes a first storage mechanism (18) which includes both the expert rule data on agenda (54) and scripts (52) which are procedurally based. Input data from the external process control system is as acquired in an acquisition system (46) where it is acquired and reduced and then inserted into a second storage system (20) where such as processed and where significant variances in data input are when output to a real time engine (100). An inference engine (16) accepts rules from the agenda (54) and outputs a second command signal to an interpreter (14) based upon the varying data and the appropriate commands from rules on agenda (54).