Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIED- 31 - AC/243(Panel-8)TR/7Volume 22.5 STATE TRANSITION DIAGRAMSWhat the technique doesSlate Transition Diagrams are extensions of data-flow analysis techniques used for the development of real-timesoftware systems. They are based on finite automata theory, and describe sequential machines which are defined asfinite state machines whose outputs are determined by both their current inputs and actual state; i.e., the machineshave memory. The memory is represented in the form of states: a sequential machine is always in one of its specifiedstates. State Transition Diagrams show the relationship between system "states" and "events" which change thesystem state. They can be used to identify operator actions needed to change the system state, and to show the effectsof human operator actions which change the system state.System states are shown as circles (Pressman, 1987) or rectangles (Yourdon, 1989) with the slate name inside,connected by arcs, which represent the transitions. The arcs can show transitions between states:They can beannotated to show the events which cause the transition, and/or the actions associated with the transition. Twodifferent types of finite state machines have been defined: one has the output uniquely determined by the states (Moorcmachine); one has the output determined by both the state and the input (Mealy machine).4 \ frdarrange I ) statno report 4 (tarnet inside radar ranae 1target detection report targetsearching taraet out of radar ranae trackingloss reporttarget inside radar rancetarget data reportFigure 2.8: States and transitions of a radar systemAnother form of visual notation for a finite state machine is the state transition matrix. The tables and diagrams arcformally equivalent, in terms of describing the system logic.Table 2.2:State table for the radar systemState Event Action Next Statetaroet searchingtarget trackingtarget inside radar range detection report target trackingtarget out of radar range no report target searchingtarget out of radar range loss report target searchingtarget inside radar range target data report target trackingNATO UNCLASSIFIED