Modelling Human Factors using the Systems Modelling Language

HFIDTC/2/WP2.8.9/1Version 2/ 24th September 2008this document has demonstrated how top level Use Cases can be brokendown using other SysML diagrams. Good SysML diagrams are unclutteredand simple to understand and this encourages an approach that breaks downcomplexity into digestible modules. The case study has also demonstrated theimportance of keeping control over the terms used to describe aspects of thedesign and how the links between different SysML diagrams promote a highdegree of integrity to the model.• It facilitates the early involvement of HF professionals: Although the earlyinvolvement of HF professionals has more to do with an efficient HFIprocess than what language is used for modelling, the use of the SysML byHF professionals may be an aid to their early involvement. This is becausethe SysML encourages the design to be documented in an iterative fashionwith an initial framework being populated to increasingly lower levels ofabstraction. It is useful to declare design intent, assumptions etc. early on sothat they are visible to a wide audience. This generates discussion andincreases the chances of eventually reaching an informed consensus. Thisapproach is likely to be of benefit to HF professionals who may otherwise beunaware of issues that impact their areas of interest. Conversely it provides agood way for HF professionals to make early declarations of their designintent and HF constraints on the design, so that these may be considered asearly on as possible.• The SysML/UML provides a convenient way of documenting a system’sdesign from the viewpoints of its stakeholders: These views can be useddirectly for, or enable the compilation of, the views required by the MODAF.SysML/UML are in fact suggested as modelling languages in the MODAFspecification. The work by the HFI DTC to promote Human Views ofMODAF adds more weight to the argument that Human Factors professionalsshould be proficient in these languages.8.2 RecommendationsThe section above has discussed the disadvantages and benefits of using theSysML/UML as a tool for HF professionals to model HF aspects of a system. It seemsreasonable to conclude that there are significant benefits and that the disadvantages canbe mitigated, and therefore it is recommended that HF professionals should give seriousconsideration to making the investment to learn and practice the SysML/UML.As to which language to chose, the UML has the advantage that it is more mature andmore widely used. If the uptake of the SysML becomes widespread amongst SystemsEngineers then this would be an argument for learning the SysML. In practice, mostexperienced modellers ‘mix and match’ the two languages, and because of the degree ofcommonality, being proficient in one of the languages will make it easy to use the other.There are several commercially available modelling tools for the SysML/UML. We didnot use any of these in the course of this study and it was outside of our scope toinvestigate their utility. We have discussed the need for an ‘index’ to link up diagrams60