SAP BW/4HANA Architecture Overview
See more in our couse BW4HANA – an Introduction
BW4HANA is optimized for HANA database.
Below figure shows the architecture of the BW4HANA system

SAP datasources can be connected via ODP framework.
Smart data access (SDA) and EIM interface provided by SAP HANA platform are used to connect any third party sources or data lake scenarios.
ETL tools in HANA can be used to transfer data to BW4HANA system.
Templates are available to do data modeling in BW4HANA, it is flexible and agile.
Data analysis can be done using SAP Business Objects or third party tools.
BW4HANA has open architecture, this means, integration of external non SAP sources and distribution of BW data to external systems using open hub service.