SYSML2 — Assignments parsed without a target will fail validateAssignmentActionUsageArguments

The approved resolution to SYSML2-28 included the adding of the constraint validateAssignmentActionUsageArguments, which requires that an AssignmentActionUsage have two arguments. However, in the SysML Specification, 8.2.2.16.5 Assignment Action Usages, the AssignmentTargetParameter is optional for an AssignmentNodeDeclaration. An AssignmentActionUsage parsed without a target parameter argument will then fail the validateAssignmentActionUsageArguments.

In 7.16.9 Assignment Action Usages it states that "If the target expression of an assignment action usage is omitted, then the target is implicitly the occurrence owning the assignment action usage." However, there is no semantic constraint enforcing this, so it is not clear how the informal statement is supposed to be realized.

Revise the validation constraint

The validateAssignmentActionUsageArguments constraint could be revised to only require an argument for the second parameter. However, it may be desirable to not bind the second parameter, either, so, e.g., the value of the parameter can be provided via a flow. So it is better just to remove the constraint all together.

The second part of the issue (on 7.16.9 Assignment Action Usages) is redundant with SYSML2-102, which has already been resolved.