Specialized requirement types

You can specify specialized requirements types by using the subtyping features of stereotypes. Systems engineers often employ use-case diagrams to define requirements.

The following example of these stereotypes can be examined in the System Samples directory in the SysMLHandset project.

• <<extend>> shows that a requirement expands or provides more detailed view of another requirement. (See Req 4.2 and 4.1 in the example.)
• <<derive>> shows a relationship between two requirements and supplies additional details. A derive requirement often reflects assumptions about the implementation of the system. (In the diagram, the arrow direction is from the derived to the original requirement.)
• <<composite>> requirements are the subrequirements within the overall requirements hierarchy. With this structure a complex requirement can be decomposed into its containing child requirements.
• <<satisfy>> relationship identifies the system or other model element intended to satisfy or fulfill the requirement. (In the diagram, the arrow direction is from the satisfying to the satisfied.)
• <<verify>> shows the relationship between a requirement and its test case. A test case is typically expressed as an activity or interaction diagram.
• <<refine>> relationship shows how a model element or set of elements further explains a requirement.
• <<trace>> requirement relationship provides a general-purpose relationship between a requirement and any other model element. The semantics of <<trace>> do not include real constraints and, as a result, is not used with any of the other requirements relationships listed previously.