UMLR — Section: 18.3.3

Section 18.3.3 states, that "An ExtensionEnd is never navigable. If it was navigable, it would be a property of the extended classifier". Whereas in section 7.3.3 (Association) on page 43, it is stated that: "Navigability notation was often used in the past according to an informal convention, whereby non-navigable ends were assumed to be owned by the association whereas navigable ends were assumed to be owned by the classifier at the opposite end. This convention is now deprecated. Aggregation type, navigability, and end ownership are orthogonal concepts [...]" The mentioned description in ExtensionEnd seems to contradict the definition of an Association. For the UML Profile Extension Mechanism two issues are essential to be clarified: 1) Is it possible, that an ExtensionEnd (which is owned by the Extension instead of the extended Class) is navigable? 2) Is it possible in a UML-Profile to define an Association which relates a Stereotype with a metaclass and which is navigable on both association ends (if the association end which refers to the stereotype is owned by the association itself instead of by the extended class)? [unidirectional Associations navigable from a stereotype to the extended metaclass seem to be allowed, as exemplified in the SysML 1.0 Standard at page 164]