Unlike with BasisCubes however, no data is physically stored in SAP BW. The data is taken from the source systems only after a query has been executed. There are three types of remote cube. They can be distinguished by the way in which they retrieve data.
Types of Remote cubes:
Virtual Cube Types -SAP RemoteCube
A SAP RemoteCube allows you to define queries with direct access to transaction data in other SAP systems.
-General RemoteCube:
A general Remote Cube allows reporting using data from non-SAP systems. The external system transfers the requested data to the OLAP processor via the BAPI.
-Virtual InfoCube with Services:
For a virtual InfoCube with services, a user-defined function module is used as the data source.
For more information you can go through the link below which will take APO/BW as an example:
https://www.sdn.sap.com/irj/servlet/prt/portal/prtroot/docs/library/uuid/5f229690-0201-0010-84ba-9ee5a8958a05
