An authoring system and method create a knowledge base for an expert system that comprises communication cells for storing external data, assertion cells for storing data acquired from a user in the course of a user dialog, and interaction cells that specify (multimedia) interactions with the user, which are carried out as the cells are invoked by the run-time program. Each interaction cell has an enabling condition that must be satisfied before it can be invoked. At authoring time, the knowledge base is constructed by an expert system author who allocates the knowledge base cells on a rectangular grid similar to a spreadsheet. The author can try out various what-if scenarios by setting the values of assertion and communication cells and recalculating the knowledge base or simulating the created expert system. The grid is only an authoring tool, which is not visible or present at run time. A preferred application of the system is to create a health care expert system that will exchange information with a health care provider.