Modelling Human Factors using the Systems Modelling Language

HFIDTC/2/WP2.8.9/1Version 2/ 24th September 2008• The Diagram Frame. Frames are mandatory for all SysML diagrams as theyallow diagrams to cross-reference to each other. There is a defined syntax fornaming Frames; they must all identify what type of diagram they contain, andthey may also identify the Model Element Type, The Model Element Name andthe Diagram Name. In Figure 7-2 the Diagram Kind is ‘UC’ to show that it is aUse Case and it has a name of ‘H-FlySystemContext’.• The System Boundary. This defines what is within the system being modelledand what is external to it. The position of the boundary has a very significanteffect on the functional requirements and an ambiguous boundary will lead toincomplete and poorly specified requirements.• Actors. An Actor represents a Role that someone or something plays in directinteractions with the system. It can also represent an entity i.e. the thing itself. It isimportant to note the difference between a Role and an entity, as it impacts uponthe design. A Role is abstract and can be allocated to an entity during the design,thus when an Actor is an entity we are showing a design decision i.e. that aspecific person, organisation, or piece of software or hardware is performing thatRole.• Use Case. A Use Case describes how an Actor uses the system to achieve a goal.• Communication Relationship. The Communication Relationship shows that theActor and the Use Case communicate in some way. When an association crossesthe System Boundary this defines an interface.16