@abc.abstractmethod<EOL><INDENT>def set_source(self, source_id):<DEDENT>
pass<EOL>
Sets the source.

        :param source_id: the new publisher
        :type source_id: ``osid.id.Id``
        :raise: ``InvalidArgument`` -- ``source_id`` is invalid
        :raise: ``NoAccess`` -- ``Metadata.isReadOnly()`` is ``true``
        :raise: ``NullArgument`` -- ``source_id`` is ``null``

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