28 coMputer systeMs/software
Standard high level modelling language aids safety systems
Matthew Hause looks at how a standard high level modelling language can help in the design and development of mission critical systems as they become standardised.
O
MG SysML provides a standard modelling language for systems engineers to analyse, specify, design and verify complex
systems through diagrams that can be used to specify system requirements, behaviour, structure and parametric relationships – the four pillars of SysML. This delivers an environment in which to design and develop mission and safety-critical systems through an inter-disciplinary approach by enhancing systems quality, improving the ability to exchange systems engineering information amongst tools and helping bridge the semantic gap between systems, software and other engineering disciplines.
In SysML the system structure is represented by block definition diagrams and internal block diagrams. A block definition diagram describes the system hierarchy and system/component classifications. The internal block diagram describes the internal structure of a system in terms of its parts, ports, and connectors while the package diagram is used to organise the model.
The behaviour diagrams include the use case diagram, activity diagram, sequence diagram and state machine diagram. A use-case diagram provides a high-level description of the system functionality. The activity diagram represents the flow of data and control between
activities. A sequence diagram represents the interaction between collaborating parts of a system. The state machine diagram describes the state transitions and actions that a system or its parts performs in response to events. The requirement diagram captures requirements hierarchies and the derivation, satisfaction, verification and refinement relationships. The parametric diagram represents constraints on system parameter values such as performance, reliability and mass properties to support engineering analysis.
A comprehensive OMG SysML Profile tool not only supports the four pillars of SysML but also further core SysML elements including requirements, blocks, constraint blocks, value types, item flows and flow ports, adding appropriate new commands, explorer panes and toolbars to the menus. Importantly, the SysML implementation allows engineers to work with SysML elements and diagrams as new element types and not just as stereotyped UML types, resulting in faster recognition, better usability and ease-of-adoption without compromising compliance to the standard. SysML artefacts can be deployed on the development of mission and safety-critical applications to specify the requirements for solution spaces such as software and hardware to provide both traceability and handover.
Requirements traceability is an essential part
Fig. 1. DoDAF screenshot from Artisan Studio.
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