16. The apparatus of claim 15 wherein the first and second graphical models each have at least one behavior, and the at least one behavior of the first graphical model differs from the at least one behavior of the second graphical model.
15. The apparatus of claim 13 wherein the first and second graphical models each model a physical system, and the apparatus further comprises means for simulating operation of the physical system modeled by one or more of the first and the second graphical models.