SysMLv1: A common misunderstanding: Just because a UseCase symbol appears inside the rectangle of a subject Classifier does NOT mean that it is owned by that Classifier and can only have that one Classifier as 'subject', and it does not imply ownership!

Graphical "containment" of a UseCase on a symbol does not imply ownership and need not always imply even being the 'subject' (although it often makes sense when it is):

UML-2.5.1: 'UseCases need not be owned by their subject.'

UML-2.5.1: 'A UseCase may be owned either by a Package or by a Classifier. Although the owning Classifier typically represents a subject to which the owned UseCases apply, this is not necessarily the case ...'

UML-2.5.1: 'Note also that the subject rectangle does not imply that the subject classifier owns the contained UseCases, but merely that the UseCases apply to that classifier.'

Some cases with Diagrams are explored here:

UseCases - UML subject vs SysML Block

Package, Model, or SysML Block as UseCase owner

GOTCHA: UML Component «subsystem» vs non-normative SysML «subsystem»

Webel: SysML for MBSE: The frequent recommendation that each UseCase have at least one "primary" scenario is a very useful and highly recommended CONVENTION (only). But it is not actually enforced by the SysML1.7 or UML2.5.1 metamodels or specifications.

SysMLv1: MagicDraw/Cameo: Having a SystemContext as the 'subject' of each main UseCase plays nicely with the feature for automated creation of usage-level allocation swimlanes in SysML Activity Diagrams for part properties. But it's not the only way.

SysMLv1: MagicDraw/Cameo: INTRINSIC GOTCHA: Care must be taken with ownership of Activities used as UseCase scenarios vs the ‘subject’ of the UseCase. Make sure you don’t get an Activity ‘context’ mismatch! It's up to you to manage it as intended.

SysMLv1: MagicDraw/Cameo: Automated creation of usage-level allocation swimlanes in SysML Activity Diagrams for part properties of a Block. EXAMPLE: A UseCase scenario within a SystemContext as UseCase ‘subject’.

SysMLv1: UseCase scenario representations: On use of Activity Diagrams with swimlanes and/or Sequence Diagrams (Interactions): Actor or block-based custom «actor» on 1st (typically left) Lifeline/Swimlane, System/Subsystem on 2nd Lifeline/Swimlane

Webel: MBSE: SysMLv1: Prefer a custom «actor» extension of a Block (such as the non-normative External) over UML-style Actor for use as parts in IBDs and on allocation swimlanes. You can also have a Trace from a block-based «actor» to a UML-style Actor.

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[UML-2.5.1] UseCase::subject : Classifier [0..*] ... The subjects to which this UseCase applies. Each subject or its parts realize all the UseCases that apply to it.

[UML-2.5.1] A subject for a set of UseCases (sometimes called a system boundary) may be shown as a rectangle with its name in the top-left corner, with the UseCase ellipses visually located inside this rectangle.

[UML-2.5.1] A UseCase may apply to any number of subjects. When a UseCase applies to a subject, it specifies a set of behaviors performed by that subject, which yields an observable result that is of value for Actors or other stakeholders of the subject.

[UML-2.5.1] UseCases need not be owned by their subject.

[UML-2.5.1] A UseCase may be owned either by a Package or by a Classifier. Although the owning Classifier typically represents a subject to which the owned UseCases apply, this is not necessarily the case ...

[UML-2.5.1] Note that this notation for the subject classifier differs from the normal Classifier notation – it has no header or compartments.

[UML-2.5.1] Note also that the subject rectangle does not imply that the subject classifier owns the contained UseCases, but merely that the UseCases apply to that classifier.

Visit also

UseCases - UML subject vs SysML Block

GOTCHA: UML Component «subsystem» vs non-normative SysML «subsystem»

Package, Model, or SysML Block as UseCase owner

Section: SysML-1.6 specification diagrams: 14 UseCases

Figure D.5 - Establishing Top Level Use Cases for the Hybrid SUV

Figure D.6 - Establishing Operational Use Cases for Drive the Vehicle

Visit also (backlinks)

External links

UML Profile: Use Case Specification for SysML Version 1.0 (2017), Raiiv Murali …

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