Abstract: A knowledge base system includes separate expert user and end user interface facilities which communicate with the system's inference engine and knowledge base. Linking means operatively interconnect the expert user facility to the end user interface facility enabling the simulation of the end user environment while the knowledge base is being concurrently edited or modified. Such simulation is carried out by placing the end user interface facility in an edit mode of operation during which the user can stop at any point. In response to a single keybgoard command, an expert user can switch control back to the expert user facility to a point within the knowledge base selected relative to the context of the operation which was being run thereby facilitating the maintenance and updating of the knowledge base.