I was just wondering if it is more correctly to as a label of objects in UML sequence diagram instead of object name (which is irrelevant in my opinion and less informative than class name) provide class name. Another thing, while returning information instead of listing all objects names would it be a better solution to just write collection;

Diagram with object names:

Diagram with class names:

As it's clearly visible from the second diagram that it is much more informative than the first one, and I think it is more practical.