Analysis Techniques For Man-Machine Systems Design

-NATO UNCLA,)irrILUAC/243(Panel 8)TR/7- 32 -Volume 2State transition matrices may be plotted as state-state tables. or as state-evenlt tables. Shown below are two versionsof the same transition matrix. The state-state table shows that, to change from state '01' to '02' requires event 'p' andproduces output "q." The state-event table shows the same logic: given event "p," the machine will change fromstate "01" to state "02" with output "q."Table 2.3: State-State Table and State-Event TableSTATETOSTATESTATEFOS t a t e 0 1FOEVENTS t a t e 02 ENT \State 01State 02xx P State 01yqqil xzzState 01 State 02_____State__02__I__IState 02Inputs to the techniqueOutputs of the techniqueThe analyst must have information on the various The technique produces diagrams of the states and statepossible system states, the inputs (events) which initiate transitions, showing the structure and relationshipsa state, and outputs (actions) which are associated with between initiating events, system states, and systemthat system state or state transition.outputs. The information can be shown in tabular form.When to use the techniqueThe technique can be used during the development of system software, following the definition of software system"tasks." It is used to define processing requirements by specifying a set of inputs and outputs, a set of states, and afunction that maps inputs plus current state onto outputs plus updated states.In human engineering analyses, state transition diagrams can be used as a task description technique, to identify thecontrol actions required of an operator, and the resultant system states and associated classes of information. Finitestate machines have been used to specify user interfaces: the input alphabet is the input from the user, and the outputalphabet is the system response.Related techniquesA related technique, the signal flow graph, shows system variables instead of states, and causal dependencies insteadof "events. Signal flow graphs have been used to analyse operator tasks in process control (Beishon, 1967). TheNATO UNCLASSIFIED- 32 -