Hi Vinay,
Create the structure like below.
Header_A1 0..1
Record 0..unbounded
Line_B 0..unbounded
ITEM_SUB_B 0..unbounded
Then after the mapping it should be like below.
Header_A1
Record
Line_B
ITEM_SUB_B
Record
Line_B
ITEM_SUB_B
Then in the FCC don't mention the Record, just use normal FCC with Header_A1, Line_B and ITEM_SUB_B then you will get required output.
Regards,
Praveen.