UML22 — Section: 9.3.5

A Property is a ConnectableElement, which currently is (should be?) a TypedElement. The Description in 9.3.5 however states: "A ConnectableElement is an abstract metaclass representing a set of instances that play roles of a classifier. Connectable elements may be joined by attached connectors and specify configurations of linked instances to be created within an instance of the containing classifier. Note on p.84 states: "When used to specify the existence of an entity in a modelled system, an instance specification represents part of that system." In 9.3.12. it says:"When an instance of the containing classifier is created, a set of instances corresponding to its properties may be created either immediately or at some later time. These instances are instances of the classifier typing the property. A property specifies that a set of instances may exist; this set of instances is a subset of the total set of instances specified by the classifier typing the property. A part declares that an instance of this classifier may contain a set of instances by composition." So, the concepts must be related. I propose that a ConnectableElement is a specialization of InstanceSpecification, not just a TypedElement. Current problems in practise: A TypedElement is not a PackageableElement and it thus cannot be imported in some other namespace. This makes is hard to create orthogonal views of architectures (e.g. logical vs. execution) in which 'roles' (parts!) are shared. On the other hand, using InstanceSpecifications instead of "Parts" makes it impossible to refer them in interactions. Besides, the meaning of an InstanceSpecification in the context of a classifier is unclear in contrast to the Property.

Discussion: The concept of connectable element is not an instance specification, so it would be a mistake to make it a specialization of InstanceSpecification. As the issue also points out, doing so would cause problems with interactions (where connectable elements are heavily used) as well as with their meaning. The issue really at hand appears to be that ConnectableElements are not packageable elements. The reason is that they have really no meaning outside of the context of the classifier they are owned by and thus would not be packaged separately. Disposition: Closed, no change