def rollback_service(self, rollback_time, proxy):
return self._provider_manager.rollback_service(rollback_time)<EOL>
Rolls back this service to a point in time.

        arg:    rollback_time (timestamp): the requested time
        arg:    proxy (osid.proxy.Proxy): a proxy
        return: (osid.journaling.JournalEntry) - the journal entry
                corresponding to the actual state of this service
        raise:  NullArgument - ``proxy`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure occurred
        raise:  Unimplemented - ``supports_journal_rollback()`` is
                ``false``
        *compliance: mandatory -- This method must be implemented.*