def is_effective_by_schedule(self):
raise errors.Unimplemented()<EOL>
Tests if the effectiveness of the enabler is governed by a ``Schedule``.

        If a schedule exists, it is bounded by the effective dates of
        this enabler. If ``is_effective_by_schedule()`` is ``true,``
        ``is_effective_by_event()`` and
        ``is_effective_by_cyclic_event()`` must be ``false``.

        return: (boolean) - ``true`` if the enabler is governed by
                schedule, ``false`` otherwise
        *compliance: mandatory -- This method must be implemented.*