Guide to Data Warehousing and Business Intelligence
The purpose of the Data Warehouse in the overall Data Warehousing Architecture is to integrate corporate data. It contains the "single version of truth" for the organization that has been carefully constructed from data stored in disparate internal and external operational databases.
The amount of data in the Data Warehouse is massive. Data is stored at a very granular level of detail. For example, every "sale" that has ever occurred in the organization is recorded and related to dimensions of interest. This allows data to be sliced and diced, summed and grouped in unimaginable ways.
Contrary to popular opinion, the Data Warehouse does not contain all the data in the organization. Its purpose is to provide key business metrics that are needed by the organization for strategic and tactical decision making.
Decision makers don't access the Data Warehouse directly. This is done through various front-end tools that read data from subject specific Data Marts.
The Data Warehouse can be either "relational" or "dimensional". This depends on how the business intends to use the information.