Transferring Data with SAP Data Services.
With SAP Data Services 4.0 and higher, you can use Data Services to transfer data to SAP BW from non-SAP sources (such as legacy systems). This is done using BW staging BAPIs. The close integration of SAP Data Services in the BW data flow concept supports DataSources of object type RSDS. Tables are supported as source objects. The source system type Data Services (specifically provided for Data Services) and the particularly close integration of SAP Data Services and SAP BW make it possible to configure a connection to external systems and to configure the transfer of external data within the Data Warehousing Workbench of the BW system. Using the Data Warehousing Workbench, you can search all the external DataStores and metadata sources in the Data Services system. You can see which tables are available in external systems and select tables for extraction. A Data Services job in the background maps the data to the BW structures. Using the InfoPackage in the BW system, you can generate a data flow between the source table and BW DataSource as a target object. You can also generate and run the extraction job and load job.
Be aware of the licensing conditions when using SAP Data Services.
DataSources (extractors) are not supported as source objects.
You can create the Data Services system as a source system. The prerequisite here is that you must first configure the Data Services system so that it can receive RFC calls from the BW system. You can perform all the rest of the steps for configuring the connection and data transfer from the BW system.
The connection with the external system - from which you want to transfer the data to BW - is created using a source data store in the Data Services system. If no source data sources are available, you can create a source data store in the Data Services system from within the BW system (while creating the Data Services source system).
More information: Creating Data Services Source Systems
Create a DataSource in BW by selecting the source table you want to extract.
More information: Creating DataSources for Data Transfer with Data Services
In the BW system, create an InfoPackage for the DataSource. This InfoPackage will be used to schedule the transfer of data into the BW system.
More information: Creating InfoPackage for Data Transfer with Data Services
You can now transfer the data from the external system to BW using SAP Data Services.
For more information about integrating with SAP Data Services, go to the SAP Help Portal at 
http://help.sap.com/bods 
<Your Data Services Release> Installation, Upgrade, Deployment 
in the Supplement for SAP guide.