Help!! - File to Idoc Mapping with Nested structure

Scenario:

I have an inbound file that has three nested records.

eg. A00, B00 and C00. C00 is nested structure of B00 and B00 nested structure of A00. All these structure can repeat N number of times in a file.

How do I map this to IDoc structure that have one segment each for the three structures in the file and nested in the same way.

Question: How is the parent child relationship established?

Suppose I have a file

A00 1234 Sam 29

B00 london LE3 XYZ

B00 US 123456

C00 2 XYZ

A00 5678 Joe 22

B00 US 23456

If I make a nested structure and then say in the file conversion properties that A00 go to segA and then B00 go to segB, but then when I come back to A00, how do I move the data to the A00?

Thanks in Advance

Rgds