A data warehouse is a collection of historical snapshots of data extracted from operational systems that is organized for easy access and reporting. Data warehouses store multiple copies of data from different points in time rather than updating existing data. The snapshots in a data warehouse are periodically refreshed with new data from operational databases to maintain an archive of historical information.

1. Presentation on Data warehouse

2. Architecture of Data Warehouse

3. Data Warehouse Overview
• A data warehouse is the concept of data extracted
from operational systems and made available as
historical snapshots for ad-hoc queries and scheduled
reporting. Characteristics that distinguish data in the
data warehouse from data found in the operational
environment are that it is: organized in such as way
that relevant data is clustered together for easy access,
several copies of the data from various points in time
are kept together, and once the data is placed into the
data warehouse it is not updated. Rather, the historical
snapshots stored in the Data Warehouse are
periodically refreshed with data from the operational
databases.