Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIED39 - AC/243(Panel-8)TR[7Volume Ikeep track of the analyses and ensure that logic requirements are maintained. SAINT, SWAT,and SIMWAM are software-based tools which require computing facilities (SIMWAM isproprietary, but is included because of its widespread use by some services).61. Human engineering analysesproduce large amounts of information. For exampie, asystem functional decomposition typically starts with seven to ten functions at the uppermostlevel. Decomposing those functions through three levels results some 1000 functions at thelower level. If the analyses are to be reviewed and reiterated (Figure 1.9) then a computer isessential to keep track of the data and facilitate modification. For these reasons, some analystsare now using relational data bases for all the human engineering analyses. The reviews ofeleven of the analysis techniques suggest that computer-based record keeping is desirable.62. Other resources which are required include information and experience. Informationfrom subject matter experts (i.e., operators or ex-operators of similar systems) is important,especially for the analyses used in early stages (Mission Analysis, Function Analysis andAllocation) and for detailed task analyses such as Decision Tables. It is also important that thehuman factors specialist be an expert in the relevant land, sea or air system andfoperations.Information on possible technical solutions, (i.e., the hardware and software to be used), is alsoimportant. All analyses benefit from experience in using the relevant technique, and functionaldecompositions in particular benefit from experience of previous analyses. A few, for example,SADT, Petri Nets, Behaviour Graphs, and SAINT. require a thorough understanding of thetheory underlying the technique.3.2.6 Advantages/disadvantages63. The reports from users of some of the techniques show that their effectiveness canvary widely between individual applications (see Section 2.1). The more general advantages anddisadvantages identified for each technique reviewed in Volume 2 also vary widely. Twocomments which appear frequently are that the analyses can become labour intensive, thereforetime-consuming, and that there is an element of subjectivity in them. This latter comment isparticularly true of functional decomposition techniques, which can be influenced by theviewpoint of the analyst. This can be seen in the examples of functional decompositions includedin Volume 2. In general, the mission and function analysis techniques are good forcommunicating with other engineering specialities (as noted in comments on Related Techniques,above), and for traceability of design features. Because these techniques try to represent what aremulti-dimensional concepts in only two dimensions, however, they present a limited view ofsystems.64. In general, the function allocation techniques are simple to perform. This advantageincurs the corresponding disadvantage that they are simplistic. Also, they can require a great dealof knowledge which is not easily available. Task analysis techniques can be fast and easy toapply, but they can become overly detailed, therefore labour intensive and hard to understand orreview. The advantages and disadvantages of performance prediction techniques are not easy tosummarize. In general they are flexible and easy to apply provided that the supporting analyseshave been completed. They suffer from a lack of demonstrated validity for many applications.The three techniques reviewed for interface and workspace design are effective for presentationand for accounting for design decisions. They can be labour intensive and subjective.3.2.7 Relative contribution65. The relative contributions made bv the different techniques are dependent on theproject phase and the type of application. For example, some types of task analysis are highlyrecommended as a basis for a Test and Evaluation Plan. The relative contribution of any one