public static function createSubClass( core_kernel_classes_Class $clazz, $label = '', $comment = '', $uri = '')
    {
        $returnValue = null;

        
		$class = new core_kernel_classes_Class(OntologyRdfs::RDFS_CLASS);
		$instance =  self::createInstance($class, $label, $comment, $uri);
		$returnValue = new core_kernel_classes_Class($instance->getUri());
		$returnValue->setSubClassOf($clazz);

        

        return $returnValue;
    }