Transform rows to columns

SELECT item_name, item_date, 
MAX(DECODE(parameter_id, '81', string_value, NULL)) Ident,
MAX(DECODE(parameter_id, '82', string_value, NULL)) USAGE,
MAX(DECODE(parameter_id, '83', string_value, NULL)) Provenance,
MAX(DECODE(parameter_id, '84', string_value, NULL)) Spec
FROM ITEM_RFRNC, ITEM_PARAMS 
WHERE ITEM_PARAMS.item_id= ITEM_RFRNC.Item_id AND
ITEM_RFRNC.item_id IN (
SELECT item_id FROM DATAPOINT WHERE group_master_id = 1661
AND variable_date > TO_DATE('5/9/2007 8:45:33 PM', 'mm/dd/yyyy hh:mi:ss PM')
AND variable_date < TO_DATE('6/1/2007 6:35:07 PM', 'mm/dd/yyyy hh:mi:ss PM')
) GROUP BY item_name, item_date
ORDER BY item_date