1) What is spro?
2) How to use in bw project?
3) What is difference between idoc and psa in transfer methods?

1.  SPRO is the transaction code for Implementation Guide, where you can do configuration settings.
* Type spro in the transaction box and you will get a screen customizing : 
   Execute Project.
* Click on the SAP Reference IMG button. you will come to Display IMG Screen.
* The following path will allow you to do the configuration settings :
   SAP Cutomizing Implementation Guide -> SAP Netweaver ->SAP Business Warehouse Information.

2.  SPRO is used to configure the following settings :
* General Settings like printer settings, fiscal year settings, ODS Object Settings, Authorisation settings, settings for  displaying SAP Documents, etc., etc.,
* Links to other systems : like links between flat files and BW Systems, R/3 and BW,  and other data sources, link between BW system and Microsoft Analysis services, and crystal enterprise....etc., etc.,
* UD Connect Settings : Like configuring BI Java Connectors, Establishing the RFC Desitination for SAP BW for J2EEE Engine, Installation of Availability monitoring for UD Connect.
* Automated Processes:  like settings for batch processes, background processes etc., etc.,
* Transport Settings : like settings for source system name change after transport and create destination for import post-processing.
* Reporting Relevant Settings : Like Bex Settings, General Reporting Settings.
* Settings for Business Content : which is already provided by SAP.

3.  PSA : Persistant Staging Area : is a holding area of raw data. It contains detailed requests in the format of the transfer structure. It is defined according to the Datasource and source system, and is source system dependent.

IDOCS : Intermediate DOCuments : Data Structures used as API working storage for applications, which need to move data in or out of SAP Systems.

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