@abc.abstractmethod<EOL><INDENT>def get_end_reference_event_id(self):<DEDENT>
return<EOL>
Gets the ``Event Id`` to which the end of this event is offset.

        :return: the relative event ``Id``
        :rtype: ``osid.id.Id``
        :raise: ``IllegalState`` -- ``has_fixed_duration()`` is ``true``

        *compliance: mandatory -- This method must be implemented.*