public static function fetchByIdentifier( $identifier )
    {
        $db = eZDB::instance();
        $identifier = $db->escapeString( $identifier );
        $stateGroups = self::fetchByConditions( array( "ezcobj_state_group.identifier='$identifier'" ), 1, 0 );
        $stateGroup = count( $stateGroups ) > 0 ? $stateGroups[0] : false;
        return $stateGroup;
    }