Abstract: A computer simulator system allows the user to specify prototype reaction to events in a pictorial manner using a visual object environment. A spreadsheet like State Table and a visual object collection coincide on a common graphical display. The State Table is filled in by pointing to lists of events or actions associated with the different objects. The contents of these lists are dependent on the object class. Event or action descriptions are transported into the respective cells of the State Table in the form of descriptive strings of text. This text describes the event or action, and the event source, or action destination. Entries in the State Table define the operation of the simulation and are executed directly by an interpreter or are compiled to generate a program of instructions for performing the simulation.