Data warehouses organize data specifically for analytical processing. Data warehousing accomplishes its objectives by denormalizing the data, reducing the number of joins, simplifying the keys, and employing the star schema.
A data warehouse is a collection of data that is extracted from one or more sources, is loaded into intelligent storage, and is optimized for the purpose of business intelligence and analytical intelligence queries and analyses. For example, a company might create a data warehouse that integrates sales, product, and customer information from various sources. This collection would help the company analyze how sales are affected by geography, by different promotions, by the gender and age of the customer, and by other factors.
A data warehouse is a subject-oriented, integrated, nonvolatile, time-variant collection of data designed to support management DSS needs. – Bill Inmen