UTP11 — Who is "self"?

What is the type/class of the instance specification called "self" in figure 6.25?

As UML says, self always refers to the context classifier of an interaction. Being applied to hwe lifeline (6.29), this implies HWEComponent being the context classifier. However, this issue leads to another one when using “self” notation: The «DefaultApplication» may point from «Defaults» among others to Package. As long as the supplier («Default») is one of Classifier, Behavior, InteractionFragment, State, Region, Activity, there is no problem. By attaching it to Package, the general idea is that such a «Default» will be applied to any test component (what represents a generic declaration and powerful application of «Default») being indirectly contained in that package. When using the “self” notation the type of such lifeline is ambiguous, because a Package never has a context classifier. Implicitly, it is seen as a generic type declaration, representing any test component/test context.