In case you want to get an overview or an idea how DataServices interacts with SAP ERP, BW,… you might want to have a look at the Wiki pages found here:
http://wiki.sdn.sap.com/wiki/display/BOBJ/SAP
Topics include:
Overview SAP Interfaces
Direct SQL
RFC-BAPI
RFC ReadTable
ABAPs
IDOCs
Connecting to SAP
Chosing the Transport Method
direct_download transport method
shared_directory transport method
ftp transport method
custom_transfer transport method
Reading via ABAP
How to read the ABAP
How to execute the ABAP
Moving to Production
Moving ABAP to Production (DI 12.1)
Common Questions
Custom ABAP Transform
[b]
Reading R3 Hierarchies
Reading via RFC Read Table
Receiving IDOCs [/b]
Building the RealTime DataFlow
Configure WebAdmin for IDOCs
Configure SAP to send IDOCs to DI
Testing the IDOCs
[b]Sending IDOCs
Calling RFCs-BAPIs
Loading BW [/b]
Setup BW - DataServices communication
Run the DataServices 3.2 RFC Server or the old method Run the DataServices RFC Server
Prepare a BW InfoSource for Loading via DataServices
Build the BW Load Job
Configure the Load Job in BW (DS 3.2) or the old method Configure the Load Job in BW
BW Load Job and datatypes
Loading BW 7.x DataSources
Reading SAP BW
Configuring SAP BW Open Hub Destination
Configuring SAP BW Open Hub ProcessChain
Reading from an Open Hub Destination
Werner Daehn 
(BOB member since 2004-12-17)