UMLR — ptc-03-09-15/Need for examples to include instance models

Issue and Recommendation: In general the specification of the Core would
benefit from instance diagrams accompanying example models, especially in
cases where there is significant change from UML 1.x. An instance diagram
accompanying an example model would show how the model instantiates the
elements of metamodel. This will contribute to a greater level of common
understanding among readers of the specification and thus will help ensure
interoperability.

For example, consider Figure 3-23 from the submission document and which
defines the abstract syntax for the elements of the
Core::Constructs::Constraints package. Despite the existence of
accompanying explanatory text, the distinction between the Namespace that
owns a Constraint and the Namespace that provides the context for a
Constraint may be difficult for the reader to grasp completely. Figures
3-24, 3-25, and 3-26 from the submission document, respectively, provide
example models. An instance diagram for at least one of the examples that
shows how the elements of the example model instantiate elements of
Core::Constructs::Constraints would go a long way toward preventing
misunderstandings. Such misunderstandings would compromise
interoperability, since there is a high probability (in my opinion) that
different implementers would render models to XMI differently.

This example is only one of many that I could cite from the submission where
examples plus associated instance diagrams would be beneficial.