In order to succeed in fierce market competition, you must have an up-to-date picture of your business. 

The challenge is how to make the best use of data in decision support. 

various analysis has to be be performed in decision support.

Online analytical processing (OLAP) consumes heavy computer resources.

Tihs is because the size of data is very large. 

This analysis cannot be carried out in an online transaction processing (OLTP) system.

Sales management system is an example of an OLTP system. 

A dedicated system needs to be built instead.  This dedicated system is called the data warehouse.