Abstract: A system for generating a control program for a target apparatus, the system comprising: a processor; a visual display unit; an input device; a program store; and a control program data store; the program store containing: an editor program for controlling the processor to accept input from the input device to modify the contents of the control program data store; a display program for controlling the processor to display a graphical representation of the contents of the control program data store on the visual display unit; and a compiler program for generating said control program from the contents of the control program data store; wherein the editor program is arranged to store control program data defining groups of sub programs for simultaneous execution on said target apparatus and control flow data defining a sequence of execution of said groups, the edit program permitting a plurality of sub programs in a group; and wherein the display program is arranged to generate a display graphically representin