Modelling Human Factors using the Systems Modelling Language

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HFIDTC/2/WP2.8.9/1Version 2/ 24th September 2008In essence the SysML is providing an alternative to represent data from traditional HFmodels produced via e.g. HTA or Operational Sequence Diagrams (OSDs). In practice itis often necessary to use a number of different representations of data or views to showhow a system functions. Building on the example above it would be beneficial to use bothan HTA and OSDs to capture and present data. HTA can be deficient in showing how andin what order multiple operators interact and is complimented by OSDs, which are builtfor this purpose. HTA and OSDs provide 2 different but valid views of the system muchlike SysML Activity and Sequence Diagrams. The key difference however is consistencybetween the data representations. When performed properly, SysML modelling demandsconsistency between views, making sure that each different viewpoint is looking at thesame thing. This inherent rigour is not necessarily ‘enforced’ across traditional HF datarepresentation techniques. The key issue then is whether the SysML can provide thevariety of consistent data representations to input to or represent the output of HFmethods and deliverables, when compared to e.g. HTA. As with HTA, SysML modellingcould underpin the human-centred design of a system and as the SysML can beunderstood by many stakeholders and is now more commonly being used to capture thewider system design, it potentially has more benefits than traditional HF methods incommunicating the human-centric views of a system design to a wider audience.A disadvantage with the SysML is that the information that represents a particular view,such as the user tasks required to operate the system, will be distributed amongst manydifferent diagrams. This could make it more difficult to read for a reader who is interestedin a particular view of the system, than say a HTA that packages that information in asingle document. However, the SysML is necessarily like this and during a system designmany stakeholders will be influencing the design of the system and therefore the model.Each stakeholder can then extract relevant views for their discipline in support of theiractivities and deliverables. Also it should be noted that even though traditional HFdeliverables may package the information, they may still be quite complex and difficultto read.50
HFIDTC/2/WP2.8.9/1Version 2/ 24th September 2008Table 8-1 - Applicability of the SysML to HFI activities and deliverablesHFI Activity orDeliverableEarly HumanFactors Analysis(EHFA)Applicability Explanation SysML Representation Applicable FiguresPartialThe SysML model of the system architecture could beused as an aid in EHFA workshops, describing thearchitecture and behaviour, to facilitate the generation ofHF Issues. Furthermore, actively generating a modelearly on will bring many HFI issues to the surface.These issues could be linked to specific parts of thearchitectural diagrams to give them context.N/A – Use SysML model creation asan input/aidTask Analysis Full Behavioural diagrams (i.e. Use Case, Sequence andActivity Diagrams) can be used to decompose high leveltasks, much like Hierarchical Task Analysis (HTA). Themajor problem in SysML when producing an equivalentto the task analysis is to have a coherent but in-depthview of system tasks. Many diagrams will be used inSysML, which together explain system behaviour. Inpractice sometimes linkages are not obvious. An HTAfor example represents all tasks in one ‘take’. HTAforms the basis for many other analysis e.g. Difficulty,Importance, Frequency (DIF), Workload, HumanReliability Assessment (HRA), thus the ease of use ofSysML diagrams as a basis for this needs to beunderstood. See suggestion below in recommendationssection on having an indexAllocation ofFunctionFullActivity and Sequence Diagrams can be used to showthe allocation of function of tasks/Roles betweenhuman/s and machines with swim lanes and lifelines.Use Case Diagrams, ActivityDiagrams, Sequence DiagramsSequence Diagrams, ActivityDiagrams, Block DefinitionDiagrams- Figure 7-3 Conduct H-FlyOperation Use Case Diagram- Figure 7-5 - Activity Diagram -Assess Request- Figure 7-4 - Sequence Diagram -Request SA Information- Figure 7-7 Expanded BlockDefinition Diagram of Posts- Figure 7-12 - Activity Diagram -Compile Tactical Picture Process- Figure 7-17 Sequence Diagram -Gather relevant information51
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Modelling Human Factors usingthe Sy
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