Analysis Techniques For Man-Machine Systems Design

NATo I UNCLASSIFEDAC/243(Panel 8'ITR/7Volume 21. INTRODUCTIONThis chapter is intended to provide users with examples of decomposition and representation of concepts, to assistin the analysis and design ot new hunan-ilnachine s stems. This is necessary because it hac been found difficultto use this approach on new systems without the benefit of reference to earlier applications. The identification of svsteifuncutons plays an important role in the svstem development process. It allows a system concept to be exploredwithout considering any hardware. software. or litcware implementation. It is the basis for developing different designconcepc. from which the app~roprate alternlative can be sclected by means of trade-off studies. System functions canalso be used as a common basis for communication between different design experts and within design teams.1.1. IMPORTANCE OF SYSTEM FUNCTIONS IN SYSTEM DESIGNAs described in Volume 1. Chapters 2 and 3. typicalIv. tie design goals for a new human-machine system are defivedfrom the operational requiremenetts which tile system has to fulfil. System functions can be viewed as broadly defilnedoperations. or activiies. which the system has to accomplish to achieve its goals. System function.s are activitieswhich produce required outputs from given inputs. When system functions are described at the appropriate levelof detail. the means for implementing them can be estahlished. At thle upper levels, the 'allocation ofTunctioLins' processincludes gross representations of huinan-inichiile system functions. for instance. 'detect trarets' and 'track tar-CIets'. These functions will be accomplished by the radar equipment and its human operator or by the sonar equipmentand its human:.operator. respectively. At lower ievels. tie process can identify tasks which the operators must perfonnwithill these systems. e.". monitor raadar screen. 'adjust sonar device'.0Functions represent one level in the hierarchy of total system activities. This hierarchy comprises various levelsof which the highest level describes system missions and the lowest level describes operator task elements (Fig I. 1).To identify relevant system functions. the alalysis slarts witi the mission of the human-machine system. By decomposingthe mission. mission scenarios and then system operations can be identified which are required for fulfillingthe mission. Finally, the partition of svstem operations leads to the system functions which are the basis for all humanengineering activities during system development. The lowest activity level which human engineers deal with isthe level of operator task elements.Functions tend to be similar for a specific class of human-machine systems. For example. destroyers, frigatcs.patrol boats all belong to the class of ship systems. A thie upper levels, ship systems can be described with the samefunctions. ncglecting differences at the detailed implementatIon levels. System designers and engineers think in termsof specific implementations. however. rather than ahstract system functions. To overcome this difficulty. it is recommendcdthat the analysis of an existing. or predecessor human-machine system. should be used as a basis for developingconcepts of future system functions and future system components. These may then be developed by consideringthe requirements of future human-machine systems. and. e.g., interpreted in terms of new technological possibilitiesfor implementation. This approach is shown in Figure 1.2. The reader should note that. despite the importance ofsystem functions. design/development leam responsibilities are usually allocated according to the system componentsor sub-systems. Project work breakdown structures (WBS) are usually a matrix of products (sub-systems) and tasks(work items or activities). Human engineering responsibilities and activities are likely to he organized on that basis.For that reason. typical system/sub-system decomposition for a work break-down structure have been included for Airforce systems (Chapt. 3.1.). Army systems (Chapt. 3.2.). and Navy systems (Chapt. 3.3.).1.2. TYPES OF ANALYSIS AVAILABLEThe analyses may proceed from one of several different viewpoints. Such a view may be system. function. orstate oriented (Table 1.1). With each view hierarchical or behavioural relationships can be considered. Theretore, ananalysis may deal with hierarchies of sub-systems. system functions, or system states. On the other hand, the analy-NATO UNCLASSIFIED2