@abc.abstractmethod<EOL><INDENT>def get_configuration_hierarchy_session(self):<DEDENT>
return<EOL>
Gets a hierarchy traversal service for configurations.

        :return: a ``ConfigurationHierarchySession``
        :rtype: ``osid.configuration.ConfigurationHierarchySession``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``Unimplemented`` -- ``supports_configuration_hierarchy()`` is ``false``

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