SYSML2 — Additional cases when usages are required to be referential

The following statements are made in Clause 7 (Language Description) of the SysML v2 specification:

• Subclause 7.6.3 (Usages): "Note also that a directed usage is always referential, whether or not the keyword ref is also given explicitly in its declaration."
• Subclause 7.13.2 (Connection Definitions and Usages): "The end features of a connection definition or usage are always considered referential (non-composite), whether or not their declaration explicitly includes the ref keyword."

However, there are currently no constraints on the Usage class in the abstract syntax to enforce these rules (see 8.3.6.4).

In addition, a usage that is not explicitly declared as a feature of a type is, by default, considered to be a feature of the base type Anything. However, since Anything is not a kind of Occurrence, its features cannot be composite. Therefore, such usages should be always referential.