Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIED- 25 AC/243(Panel-8)TR/7Volume 2la-yInputs to the techniqueInformation on system context (why the system isrequired) is needed to initiate the analysis. The analystsmust obtain information on system functions, inputs,controls, outputs, and design and operating constraints,as they proceed through the analysis.Outputs of the techniqueThe output of the technique is a system requirementsspecification, including SADTr diagrams, which showthe system functions, the function inputs, controls.resources, and outputs, and the logical flow of informationand material between them. The specification thusidentifies the mechanisms needed for the system concept.When to useBy definition, the technique is most suitable for the requirements definition phase of a project, (the preliminarysystem studies phase and concept formulation). This can include the requirements definition for-acomputcrsimulation such as SAINT (5.2) or other networking models, which can occur later during system development Thetechnique can also be used to document an existing system prior to upgrade.For human engineering purposes the technique could follow a mission analysis, or be derived directly from thestatement of requirements. It should precede detailed tasks analyses and workload analyses. If SADTr' is being usedfor system software development, then it may be possible to use it as the basis for human engineering studies.AdvantagesDisadvantagesSADTIm supports the systematic definition ofSADTr diagrams show only the input and output flowrequirements. It provides a management and accounting between functions. They do not show sequential functiontool, and is an effective way of obtaining consensus about flows or times. Thus SADT'" does not provide all ofthe requirements for a project Wallace, Stockenburg and the information required to produce a network model ofCharette (1987) argue that SADT"1 is the first of three operator tasks (see Floyd. 1986). Additional analysis isessential steps in a unified method for developing systems. necessary.The technique permits the specification of systemrequirements with the minimum of redundancy. Itrepresents the allocation of resources within a system, andprovides an effective basis for trade-off decisions, to studyfuture system capabilities and improvements, and toidentify system tasks and task dependencies. Thedocumentation of function resources also facilitates thestudy of reversionary-mode operation, because the impactof the "failure" of a specific resource can be studied easily.Related techniquesThe recommended limit of not more than six boxes perlevel can limit the scope of the representation, so that, atlower levels, concurrent functions may not berepresented on the same diagram.One user cautions that the "viewpoints" used to developthe requirements are not unique. Thus the analysisreflects a specific viewpoint, and could be biased.SADTrm is a development of the basic form of function analysis. The Controlled Requirements Expression (CORE)technique developed and used in the UK is closely related (System Designers, 1986). Also related are the StructuredDesign approach of Yourdon (1989), Structured Analysis of De Marco (1979), Essential System Analysis ofMcMenamin & Palmer (1989), and Information Systems Work and Analysis of Change (ISAC) developed byStockholm University (Lundeberg, Goldkuhl, & Nilson, 1981).NATO UNCLASSIFIED- 25 -