Hierarchies in SAP

Hi

I am reading hierarchies from R/3 using tables-

1) SETHEADER

2) SETLEAF

To form a hierarchy.

Example-

4FM_WF_ALL is the Root found in the SETHEADER Table.

Belongs to CLASS-0000, TYPE-S, TABLE-FMRBSC, FIELD- WFSTATE_9

The leaf for the above root has the following values from the SETLEAF Table.

FROMVALUE- P, TOVALUE-P, LINEID-000000001.

1) What are these hierarchies?

2) How are the entries made in tables SETLEAF and SETHEADER?

3) What is the use of such hiearchies?

4) Any documents supporting will be appreciated.

Thanking you in advance,

Ps: Points will be awarded for your time and solutions.