Abstract: The system providing a guidance for the command entry to an interactive computer recognizes the hierarchical rank of productions and displays command explanatory messages below the rank of production to which the command in need of explanation belongs. Displaying commands of one or two ranks relieves the operator from the annoyance of useless display reading.

Abstract: In an inference machine having a knowledge set portion which stores therein a set of knowledge items such as rules, and an inference portion which interprets the rules for execution; priority level information items which set precedence degrees among the rules within the rule set are stored in a plurality of series with respect to standpoints of users, one series which meets the standpoint of a particular user is selected from among the plurality of stored series of priority level information items, and the rule of the highest precedence degree is selected on the basis of the selected series of priority level information items, with the result that the rule conforming to the standpoint of the particular user is selected and executed.