@abc.abstractmethod<EOL><INDENT>def get_repository_hierarchy_design_session(self):<DEDENT>
return<EOL>
Gets the repository hierarchy design session.

        :return: a ``RepostoryHierarchyDesignSession``
        :rtype: ``osid.repository.RepositoryHierarchyDesignSession``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``Unimplemented`` -- ``supports_repository_hierarchy_design()`` is ``false``

        *compliance: optional -- This method must be implemented if
        ``supports_repository_hierarchy_design()`` is ``true``.*