SAP BW has three layers:

• Business Explorer: As the top layer in the SAP BW architecture, the Business Explorer (BEx) serves as the reporting environment (presentation and analysis) for end users. It consists of the BEx Analyzer, BEx Browser, BEx Web, and BEx Map for analysis and reporting activities.
  
• Business Information Warehouse Server: The SAP BW server, as the middle layer, has two primary roles:
  • Data warehouse management and administration: These tasks are handled by the production data extractor (a set of programs for the extraction of data from R/3 OLTP applications such as logistics, and controlling), the staging engine, and the Administrator Workbench.
  • Data storage and representation: These tasks are handled by the InfoCubes in conjunction with the data manager, Metadata repository, and Operational Data Store (ODS).
  
• Source Systems: The source systems, as the bottom layer, serve as the data sources for raw business data. SAP BW supports various data sources:
  • R/3 Systems as of Release 3.1H (with Business Content) and R/3 Systems prior to Release 3.1H (SAP BW regards them as external systems)
  • Non-SAP systems or external systems
  • mySAP.com components (such as mySAP SCM, mySAP SEM, mySAP CRM, or R/3 components) or another SAP BW system.