@abc.abstractmethod<EOL><INDENT>def get_root_catalogs(self):<DEDENT>
return<EOL>
Gets the root catalogs in the catalog hierarchy.

        A node with no parents is an orphan. While all catalog ``Ids``
        are known to the hierarchy, an orphan does not appear in the
        hierarchy unless explicitly added as a root node or child of
        another node.

        :return: the root catalogs
        :rtype: ``osid.cataloging.CatalogList``
        :raise: ``OperationFailed`` -- unable to complete request
        :raise: ``PermissionDenied`` -- authorization failure

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