@abc.abstractmethod<EOL><INDENT>def get_schedule_start(self):<DEDENT>
return<EOL>
Gets the start date of this schedule.

        If ``has_time_period()`` is ``true,`` the start date is the
        start date of the associated ``TimePeriod``.

        :return: the start date
        :rtype: ``osid.calendaring.DateTime``


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