@abc.abstractmethod<EOL><INDENT>def get_exception_ids(self):<DEDENT>
return<EOL>
Gets the exception ``Ids`` to this time period.

        Recurring events overlapping with these events do not appear in
        any recurring event for this time period.

        :return: list of exception event ``Ids``
        :rtype: ``osid.id.IdList``


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