Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFTED- 23 - AC/243(Panel-8)TR/7Volume 22.3 STRUCTURED ANALYSIS AND DESIGN TECHNIQUE (SADTr)What the technique doesSADTrm. and its military equivalent IDEF®, were developed to describe complex systems and control thedevelopment of complex software through a systematic approach to requirements definition (Ross & Schoman,1977). One of the aims was to develop a process which includes definition of human roles and interpersonalprocedures as part of the technique. SADTr" (or IDEF) approaches requirements definition through a series of stepswhich determine why the system is needed, what the system features will serve, and how the system is to beconstructed. The requirements are defined by identifying the necessary functions, and developing an implementationthat meets the requirements by performing the functions (see Marca & McGrowan, 1987, for example).The technique has been adopted to describe complex systems which may include any combinationef hardware.software, and people. It is also being used to describe systems for computer simulation, or modelling. A SADT'adescription of a system consists of diagrams, text, and a glossary, cross-referenced to each other. The description isorganized into a hierarchy of interconnected diagrams. The top level of the hierarchy contains the most generaldescription of the system: the bottom level contains the most detailed description.Diagrams are the principal means of representation. AllControlssystem functions (activities, actions, processes. operations)are represented as boxes, and interfaces are represented byarrows. The positions at which an arrow enters a box Inputs Outputsconveys the role of the interface. Conditions which govern System Dthe function (controls) enter the top of the box. Materials. -- >- Functionor information acted on, enter the left side of the box. Themechanism (person or equipment) which performs thefunction enters the bottom of the box. The output of thefunction leaves the right side of the box.Mechanisms(processors)Figure 2.4:Basic SADT DiagramMission Briefingdata materialDoctrine, Tech.tactics odrSensor ino. I Mission resultsFuel Perorm CommunicationsWea pons aircraft mission CFigure 2.5:AircrewAircraft systemsTop level SADT function for an aircraft missionNATO UNCLASSIFIED-23 -