SysML: Syntax ain't Semantics: FUN CHALLENGE: SysMLv1 block property aggregation: 'The tornado chaser plane "has" a chaser car "with" a chaser team.'

The 'has' and 'with' in the text statement have both been interpreted as 'composite' aggregation, so the poor people corresponding to the part :ChaserTeam, which has 'composite' aggregation as a part within :ChaserCar (itself incorrectly modelled as a 'composite' part within the ChaserPlane Block), are now stuck up in the sky in a flying along with the :ChaserPlane (as shown here using instances)!

The ChaserTeam is a custom SysML-style block-based "actor" with the Stereotype keyword «actor»:

Webel Best Practice: 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.

So although use of AggregationKind 'composite' for :ChaserTeam is not semantically correct here, it is syntactically allowed in SysMLv1, as often used for "actor parts" in SystemContext IBDs.

SysMLv1 has aggregation kind 'shared'. That lends itself perhaps to the 'with' in 'chaser car with a chaser team' for :ChaserTeam within the ChaserCar, and might given them a way out of their predicament.

But it's that use of 'composite' for :ChaserCar for 'The tornado chaser plane has a chaser car' that has caused them big trouble. The :ChaserCar is now a part of the plane, hence its scary appearance up in the sky carried along by the flying chaser plane that is chasing a tornado!

The solution? Use a reference property instead with AggregationKind 'none' for :ChaserCar within ChaserPlane.

Officially in SysMLv1:

SysMLv1.6: 'A property typed by a Block that does not have composite aggregation is classified as a reference property.'

SysMLv1.6: 'SysML also supports properties with shared aggregation, as shown by a white diamond symbol on an association.'

But informally the term shared property is used, although it does not appear in a separate compartment from references on SysMLv1 Block symbols.

Visit also: UML2/SysML1.x: If AggregationKind 'shared' has meaning to you (and if you use it consistently without contradicting the use of 'composite' aggregation elsewhere in your model) by all means use it. Damn the purists! But it's going to die in SysMLv2 anyway.

Visit also: SysML1.x: MagicDraw/Cameo: The shared property concept is implemented using a vendor-specific stereotype extension SharedProperty

Visit also: REFERENCE CARD: Property cheat-sheet for Block

Visit also: REFERENCE CARD: Types of Block Properties and Block compartments

Visit also: SysML "shared" Property example: two Triangles share one LineSegment edge.

Visit also: SysML "shared" Property challenge as objects: two Triangles share one LineSegment edge.

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