SYSML21 — Validation of the definition of an item usage or part usage

In 7.10.2 Item Definitions and Usages, it states:

An item usage must only be defined by item definitions (of any
kind) or KerML structures (see [KerML, 7.4.4]).

Similarly, in 7.11.2 Part Definitions and Usages, it states:

As a kind of item usage (see 7.10), a part usage must only be
defined by item definitions (including part definitions) or KerML structures (see [KerML, 7.4.4]).

However, there are no formal validations in the abstract syntax supporting either of these statements.

In the abstract syntax, the property ItemUsage::itemDefinition subsets OccurrenceUsage::OccurrenceDefinition, it does not redefine it (see 8.3.10.3 ItemUsage). Similarly, the property PartUsage::partDefinition subsets ItemUsage::itemDefinition. Therefore, the model allows the definitions of both item and part usages to include OccurrenceDefinitions (or KerML Classes) as well as ItemDefinitions (or KerML Structures). And there are no validation constraints in ItemUsage or PartUsage to further restrict this.