@abc.abstractmethod<EOL><INDENT>def set_effective_date(self, date, rate):<DEDENT>
pass<EOL>
Sets the effective date.

        :param date: a date
        :type date: ``timestamp``
        :param rate: the rate at which the clock should tick from the given effective date. 0 is a clock that is fixed
        :type rate: ``decimal``
        :raise: ``NullArgument`` -- ``date`` is ``null``

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