Characteristics of Data Warehouse A data warehouse is

Characteristics of Data Warehouse • A data warehouse is a repository of subjectively selected and adapted operational data, which can successfully answer any ad hoc, complex, statistical or analytical queries. • It is situated at the centre of a decision support system (DSS) of an organization and contains integrated historical data both summarized and detailed information common to the entire organization.

• Data warehousing technology is becoming essential for effective business intelligence, business strategy formulation and implementation in a globally competitive environment. • Data warehousing enables easy organization and maintenance of large data in addition to fast retrieval and analysis in the manner and depth required from time to time. • Data can be classified into three categories: 1. Reference and Transaction Data 2. Derived Data 3. Denormalized Data

• Reference and Transaction Data 1. Originates from operational (source) systems and is normally kept in a conventional database system. 2. It is loaded for refreshing the data warehouse. 3. If it is purged from the source then it is archived into a data warehouse. 4. Once put in a data warehouse, it cannot be modified

• Derived Data 1. It is derived from reference and transaction data, based on certain rules or computations. 2. It can always be derived again on fresh or modified basis of derivation. • Denormalized Data 1. It is the basis for Online Analytical Processing (OLAP) tools, is prepared periodically but is directly based on detailed (transaction) reference data.