@abc.abstractmethod<EOL><INDENT>def is_effective_by_schedule(self):<DEDENT>
return<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: ``true`` if the enabler is governed by schedule, ``false`` otherwise
        :rtype: ``boolean``


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