Abstract: A knowledge base processor is callable by an application program to access a knowledge base and to govern the execution or interpretation of the knowledge base to find the values of selected objects or expressions defined in the knowledge base. The application program is written in a conventional computer language which specifies control by the ordering of program steps. The application program provides a user interface for input/output and provides top level control for calling the knowledge base processor to find values for goal expressions. During its search for the values of goal expressions, the knowledge base processor calls the application program to determine values of expressions which are not concluded by the knowledge base, and to signal important events during the execution of the knowledge base. Preferably the knowledge base processor and the application program each include a library of subroutines which are linked-loaded to provide a complete knowledge system for a specific application or task.