SYSML17 — Reference Properties do not reference properties

A reference property of a Block may only be typed by (i.e. "reference") another Block. There is no current mechanism for a reference property to explicitly reference a part property of a different block. See Figure D.16 for example; the PowerSubsystem Block is assumed to be referencing the part property of the BrakeSubsystem typed by BrakePedal. This is a logical conclusion since there is only one part property typed by BrakePedal, but if there were multiple part properties typed by BrakePedal, the reference property of the PowerSubsystem Block would be ambiguous.

Practical use of reference properties has consistently implied that a particular part property CAN be referenced (i.e. "a part property owned by another block"), but no mechanism for this is explicitly provided in SysML. Also, there does not appear to be any constraint on instance semantics of reference properties that might clarify this ambiguity at the instance level.

See also SYSML16-42 and SYSML16-228.

Proposal: Reference properties do not reference properties

Discussed during May 16th, 2019, RTF meeting:

We believe that the requested capabilities are already provided by the current SysML version. There are multiple ways to represent such constructs:

1. A binding connector and optionally a BoundReference property can be used
2. Derived attribute and/or an operation
3. Specific properties that subset the collection (assuming the types of the properties owners conform to one another)
4. Using proxy ports with appropriate connectors