Replacing an object in an object oriented model in a computer system, by interrogating the model to retrieve information defining the relationships between the object to be replaced and other components of the model is described. The motor vehicle includes, but is not limited to a coupling device designed for connecting the motor vehicle to a trailer. The plant also includes means for supplying solids and gas feed materials to the vessel and for tapping molten material from the vessel. An input device tray is rotatably connected to the cabinet, and has i) an operating position that holds computer input device in an input position and ii) a stowed position substantially preventing access. The conduction region includes a plurality of implant regions, arranged at respective depths from the surface of the drift region.