The semantics of graphical input
Ed Anson · 1979
Any graphical input device may be represented by a data structure, modified from time to time by actions in response to certain events, and the ability to cause certain events as part of its repertoire of actions. Portions of a device's state may be made visible to other devices in a controlled way, and the remainder hidden. Conversely, a device may make use of the visible portions of another device's state. Typically, the pattern of device interaction forms a hierarchy, but no device is part of any other. This provides for the interchangeability of a single device with a group of devices, and allows a single device to support the function of several others. Device independence is thus enhanced without the usual sacrifice of human factors considerations.