List all the attribute classes of image ID 22.
attribute classes of image ID 22 refer to ATT_CLASS where MG_ID = 22;
SELECT T1.ATT_CLASS FROM ATT_CLASSES AS T1 INNER JOIN IMG_OBJ_ATT AS T2 ON T1.ATT_CLASS_ID = T2.ATT_CLASS_ID WHERE T2.IMG_ID = 22