SAP has given the option of migration of hierarchy to 7x flow with SAP BW 7.3 release. This document explains how to do the migration of it using step by step approach with screen shots.
Note: SAP has given the new T. Code RSMIGRATE to do the migration of 3.x flow to 7.x (lots of documents are available on SCN) but hierarchy migration is not feasible using this toll, whereas one need to go with manual steps only.
1. Migrate the datasource into 7x
Use button with export as it provide option to revert back to 3x in future
2. Create Transformation
This will automatically create required data mapping. You will find dropdown like Source Segment/Target Segment which will take care of various hierarchy data flow mapping like header, Text, Node, Node text and interval (if any).
3. Create DTP :
Finally load the infopackage and run the DTP to load data into Hierarchy.
Hope this will be helpful for migration of Hierarchy into 7x flow.