mapping issue

My scenario is FILE to IDoc:

ORDERS05 - ORDERS IDOC

-IDOC

--E1EDP01 - ITEM DATA

---E1EDP02 - SCHEDULE AGREEMENT ITEM DATA

-

E1EDP02-BELNR - BELNR

---E1EDP20 - SCHEDULE LINE ITEM DATA

INPUT FILE IS:

HEADER 1:1

-ITEM 1:UNBOUNDED

--ITEM1 1:UNBOUNDED

---ITEM1-UNIQUEIDENTIFIER

Whenever a new E1EDP02-BELNR ORDERS05 idoc should be created.

Example:

E1EDP02-BELNR = 10000

E1EDP02-BELNR = 10000

then only one IDoc should be created

E1EDP02-BELNR = 10000

E1EDP02-BELNR = 10001

then two Idocs should be created with two BELNRs...

How to acheive this in mapping...