DB2 OLAP Server can work with a data warehouse that is built from a relational database and configured as a star schema. You can use the star schema as a data source for DB2 OLAP Server, but you cannot use the star schema directly as a DB2 OLAP Server relational cube.
Loading data into DB2 OLAP Server enables you to take advantage of the DB2 OLAP Server calculation capabilities. Using DB2 OLAP Server to calculate summary data is easier than using SQL procedures.