[BR-30]-If both Invoice line period start date (BT-134) and Invoice line period end date (BT-135) are given then the Invoice line period end date (BT-135) shall be later or equal to the Invoice line period start date (BT-134).
Stored validation assertion
(ram:EndDateTime/udt:DateTimeString[@format = '102']) >= (ram:StartDateTime/udt:DateTimeString[@format = '102']) or not (ram:EndDateTime) or not (ram:StartDateTime)