@abc.abstractmethod<EOL><INDENT>def search_among_relationships(self, relationship_ids):<DEDENT>
pass<EOL>
Execute this search among the given list of relationships.

        :param relationship_ids: list of relationships
        :type relationship_ids: ``osid.id.IdList``
        :raise: ``NullArgument`` -- ``relationship_ids`` is ``null``

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