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Elements Associated with Use Cases

Component “Actor”

involves (participates in)

describes (described by)

extended by extends)

includes (included in)

UseCase

decomposed by (decomposes)

elaborated by elaborates)

elicits (elicited by)

refined by (refines)

Function ProgramActivity TestActivity

Requirement

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SysML Use Cases

• Is the highest level of abstraction for a system • Is used to identify or discover requirements and system contexts.

• Describes a system requirement (primarily functional) from an actor’s perspective • Represents the interactions between the System and its external “Actors” or Components • Emphasizes functionality rather than control or timing—implicit is the discovery of functional requirements. • Must provide observables to the actor • Viewed by some as the easiest diagram to get wrong!*

*  Holt and Perry, SysML for Systems Engineering, 2008, p. 154

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