1. A method of operating a computer system for generating a human-computer interface prototype, the computer system including a display and means for indicating an x,y location on the display and generating an asynchronous event, comprising the steps of: a. describing an interface prototype in a high-level graphics language having a command for describing a graphic object that creates a graphic item on the display and links a specific behavior to the graphic item in response to an asynchronous event occurring within the graphic item, the object being defined independently of the x,y location of the graphic item on the display; b. compiling the high-level graphic language description to produce an intermediate low level code optimized for interpretation; and c. interpreting the intermediate lowlevel code produced in the previous step to implement the prototype interface.