MODEL OF INTERACTION

The interaction is between the program and the user.
-- The user inputs information via the input devices.
-- The program outputs information via the output devices.
-- The user and program actions are asynchronous relative to each other except where explicit synchronization is needed.
-- NOTE the program-centric nature of this "input/output" terminology.

The value returned by an input device is called its measure.
-- E.g., keyboard measure = ascii strings.
-- E.g., mouse measure = (x,y) position.

The mode of transfer of measures from input devices to the program can be classified using two criteria:

Whether the transfer is initiated by the program or by the device.
Whether the transfer is triggered by the program or by the device.

NOTE: The transfer is assumed to take place very soon after a trigger. However, there is a undetermined time gap between initiation and triggering, depending on the mode.