What is Data Warehouse ?

The term Data Warehouse was first coined by Bill Inmon in 1990, and he defined in his way like, A Data Warehouse is a Subject Oriented, Integrated,Time-Variant,and Non-Volatile collection of data in support of management's decision making system.

Each Term in Detial...

What it means by Subject-Oriented?
- > Data that gives the information about particular subject instead of company's ongoing process.

What it means by Integrated ?
- >Data that is gathered into a warehouse from the different source and merged into a coherent whole.

What it means by Time-Variant ?
- > All the data in the data warehouse is identified with a particular time period.

What it means by Non-Volatile?
- > Data is stable in the data warehouse.More data is added but never removed from it.This enables the management the consistent picture of the business.


This defenation remains reasonably accurate almost till now. However single subject data warehouse is typically referred to as data mart, while generally data warehouse keeps the whole enterprise in scope.Also data warehouse can be volatile.Due to large amount of storage required for a data warehouse,only a certain number of period of the history are kept in to a warehouse.

Let's say for an example,If 3 years of data are decided on and loaded into a warehouse so every month the oldest month will be rolled off the database and newest month will be added.

(Source: "What is a Data Warehouse?" W.H. Inmon, Prism, Volume 1, Number 1, 1995).