UML22 — Allowing multiple Associations in a Package with the same name

I had a recent ‘argument’ with Steve Cook on his blog. There is a lot of confusion with regards to whether there can be multiple Associations with the same name in a Package. Steve made the valid point that Association does not redefine “isDistinguishableFrom”, which it gets from being a NamedElement. This is overridden for BehavioralFeature, but not for Association, thus based on that rule from NamedElement, I assume that there may not be multiple Associations with the same name (including empty) in a Package.

However, I came across the following cases that seem to ignore this notion:

1) In the rules for PackageMerge (7.3.40), they allow for the ability to have multiple Associations with the same name by taking into account their member ends: “Elements that are a kind of Association match by name (including if they have no name) and by their association ends where those match by name and type (i.e., the same rule as properties).”

2) The MOF 2.0 XMI file almost never names its’ Associations, thus having many Associations with the same name.

3) The UML 2.1.1 Superstructure XMI file also has multiple associations with the same name. As an example, see the package with id “AuxiliaryConstructs-Templates”. It owns 3 associations with the name “A_templateParameter_parameteredElement” (ids “A_templateParameter_parameteredElement”, “A_templateParameter_parameteredElement.1” and “A_templateParameter_parameteredElement.2”).

Is it intended that multiple Associations with the same name be allowed in a Package or not? If not, then we need to fix Superstructure, MOF, and we can also relax the PackageMerge rule for Associations. If we do allow it, then we should add a new redefinition of “isDistinguishableFrom” for Association that specifies a similar rule to the one described in PackageMerge, that an Association type is distinguishable from another Association if the set of its name and the names of all its member ends is not equal to the corresponding set of the other Association.

A redefine of isDistinguishableFrom for Association is not desired. As such, the PackageMerge rule for Association, which implies the possibility of multiple Associations in a Package with the same name, including if they have no name, provided their member ends differ in some way, is to be amended as it can result in ill-formed merged Packages. This is supported by the following 2 constraints:

1. MOF 2.0 Specification, under section "12.4 EMOF Constraints" there is the following constraint (which would be violated if the Associations have no name):
"[3] Names are required for all Types and Properties (though there is nothing to prevent these names being automatically generated by a tool)."

2. In "9.14.2 Namespace" of the UML 2.1.2 Infrastructure Specification there is the following constraint (which would be violated if the Associations have the same name):
"[1] All the members of a Namespace are distinguishable within it."

As such, explicit rules are also to be added to PackageMerge requiring well-formedness of the merged Package.

The XMI elements cited as examples of clashing Association names are to be renamed.