UMLR — UML 2.5 issue. AssociationClasses should have isUnique property

Dragan Milicev’s paper at http://afrodita.rcub.bg.ac.rs/~dmilicev/pubs/mdd/trumlassoc.zip points out that AssociationClasses can be multiply instantiated between the same set of end instances, even when all the ends are marked as unique. He proposes adding an isUnique property to AssociationClass to distinguish between circumstances where this is allowed and those where it is not.