Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIED39 AC/243(Panel-8)TR/7Volume 21.e)theH2.7 BEHAVIOUR GRAPHSWhat the technique doesBehaviour graphs are combined control and information flow graphs for describing system behaviour within theRequirements Driven Development (RDD) systems engineering methodology (Alford. 1985b; Kloster & Tischer,1987; Lenorovitz & Phillips, 1987). The graphs show system behaviour explicitly as a function of time. The dataflow is shown on the horizontal axis, and time on the vertical axis. The graphs are used for function analysis at thesystem level, and for scenario modelling.The basic language element of behaviour graphs is the discrete function. A discrete function inputs one (Out of severalpossible) discrete items, and outputs one (or several) discrete items. The transformation is triggered by the arrival ofdiscrete item. The transformation can also be based on state information. The discrete function may have severalexit paths. One exit path is selected, based on conditions from the transformation. The transformation of the discretefunction includes both a mapping between the input and output items (interpreted as symbols) and a transformation ottheir contents. The transformation has specified performance indices. The formal description of this transformation isregarded as a software engineering responsibility, and is not described here.In its graphical representation, the discrete function is visualized as a shaded rectangle. discrete items as ovals, andstates as shaded ovals.data flcw --screte time |state,itemunction'n.' 'sat..Figure 2.11:Graphical representation of a discrete functionSequences and "concurrencies" of discrete functions are described by control constructs. The control constructs areselection, loop, iteration, GOTO, concurrency, and replication (copies of functions that are performed concurrently).A graph of discrete functions (called an F-net) can be aggregated into a timefunction. Time functions are also usedfor modelling of continuous transformations. A timefunction is visualized as a rectangle. The top level systembehaviour consists of one single time function. This function is then refined (decomposed) into a graph of new timefunctions and/or discrete functions. This process is repeated until every time function has been decomposed intodiscrete functions.Sequences and concurrencies of discrete items are described by the same control constructs as used for the functions,except for loop and GOTO. A graph (I-net) of discrete items can be aggregated into a time-item.NATO UNCLASSIFIED- 39 -