Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIED75 -AC/243(Panel-8)TR/7Volume 24.3 OPERATIONAL SEQUENCE DIAGRAMS (OSDs)JyWhat the technique doesoperational Sequence Diagrams are extended forms of Flow Process Chart (4.2) which provide a graphic presentationof the flow of information, decisions, and activities in a system, using a set of five basic graphic symbols and anassociated grammar. The technique is tailored for the representation of the flow of information, with symbols for thetransmissionf receipt, processing, and use of previously stored information. The diagrams show the sequence of tasksor actions in a vertical sequence: they can be annotated with time information or a time line.The technique is very much an integrative one, pulling together information derived from other analyses. OSDs canbe used to represent the task of a single operator or of multiple operators interacting with a system (see Brooks,1960; DeGreene, 1970; Henry et al., 1968; and Laughery & Laughery, 1987).The diagrams show how the operators interact with thesystem, the sequence of activities. and any branches orloops. The OSD can be used for developing the human-machine interface, for evaluating them, for developingoperational procedures and identifying critical conditionswith regard to concurrent operations.Inputs to the techniqueInformation on the tasks performed by the operators.their sequence, and the processing tasks performed bythe system are inpuL System decompositions andfunction allocations generally provide sufficientinformation to start the analysis.Outputs of the techniqueWhen to useThe analysis is a logical successor to function allocation analysis for complex systems. It can be used frompreliminary system studies through to design and dcevlopment. It precedes workload analysis. OSDs also form a goodbasis for the development of SAINT simulations (5.').RelatedtechniquesOSDs are related to Flow Process Charts, and to other industrial and software engineering charting techniques such asthe Merise technique (Tardieu, Rochfeld, & Colletti, 1989).SAINT simulations (5.2) can produce OSDs as output, although the more usual practice is lo use OSDs to generatethe SAINT network.Resources requiredOSDs can be produced manually. This is not recommended, due to the workload associated with editing changes. Acomputer-based method is preferable. Very simple computer techniques have been used (Lahey, 1970: Larson &Willis, 1970). Such computer representations should not reduce the OSD to a simple tabular task analysis, therebylosing the advantage of the graphic representation of interactions.NATO UNCLASSIFIED- 75 -