Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSI FI7ED- 19- AC/243(Panei-8)TR/7Volume 2velAdvantagesDisadvantagesBlock diagrams are widely used to communicate ideas The technique requires a good understanding of typicalabout the structure and logic of systems. Users report that system functions. Although the technique is easy tothe technique is very effective for communicating system learn, it is is beneficial to have available function!d in function requirements to potential users. The diagrams are decompositions from similar systems. Thus there is aalso useful for communicating with other members of the "start-up" cost if the user has no previous experience.design team. The technique is generally found to be aahighly effective way of identifying system requirements, at The diagrams show only the logical or chronologicalIs.the outset of design. It is simple to learn, and is not labour sequence of functions. They do not contain the inputsintensive, unless all diagrams are prepared by hand. and outputs of system functions, or show the inputoutputflow. They do not show the informationThe systematic decomposition of the system functions, pertaining to decisions or time and time-criticalcoupled with the reference numbering system provides activities.m, rationalized traceability from lower to higher levelfunctions, and between functions at the same level. The Function flow diagrams are not an end in themselves:function analysis can be used to study reversionary-mode they are not suitable for inputs to detailed systemoperations. by examining the impact of removing specific requirements which involve human operators, but mustfunctions.be used as a basis for further analyses.7).Y. Quality assurance considerationsNovice users have shown some difficulty in keeping each level of analysis consistenL Because the number offunctions increases exponentially with the level of detail, it is easy for inconsistencies to occur at the lower levels. Acomputer daa-base is recommended for maintaining consistency of terms, numbering, and application of theindividual functions.Woodson (1981) cautions that what purports to be function analysis is often the description of aconcept. Thus terms such as "data entry unit" or "drum storage" are used. instead of descriptions of what has to bedone. Guidance for the preparation of FFDs is contained in a US Air Force Data Item Description (USAF, 1971.a):although not widely referenced. it still may be written into contracts.. pRelationship to system performance requirementsFFDs are indirectly related to system performance requirements They can be related to the system performancerequirements via the mission analyses. The functions define what the system must do to perform the mission.Referencesand BibliographyAide)ard1. Laughery, K.R. Snr., Laughery, K.R. Jr. (1987). Analytic techniques for function analysis. In: G. Salvendy (Ed.),Handbook of human factors. New York: John Wiley & Sons.2. Lurcott, E. (1977). F2D2 (Functional flow diagram and descriptions), a system management tool. DefenseSystems Management Review (1), 19-28.3. Nice, J.A. (1984)..A system designer's view and use of human factors. In: Workshop on apnlications of systemsergonomics to wearons system develooment. Volume 1: Technical Papers. Brussels: NATO. DS/A/DR(84)408.4. USAF (1971.a) Data Item Descrirlion -Functional flow diagrams. DI-S-3604/S-126-1. Washington D.C.: U.S.Air Force Systems Command.5. USAF (1971.b). Data Item Descriotion - Requirements Allocation Sheets. DI-S-3605/S-127-1. Washington D.C.NATO UNCLASSIFIED- 19-