A database, frequently very large, that can access vast arrays of heterogeneous data, stored within a single logical data repository, that are accessible to different querying and manipulation methods . While the warehouse can be distributed over several computers and may contain several databases and information from numerous sources in a variety of formats, it should be accessible through a server. Thus, access to the warehouse is transparent to the user, who can use simple commands to retrieve and analyse all the information. The data warehouse also contains data about how the warehouse is organized, where the information can be found, and any connexions between data. Frequently used for decision support within an organization, the data warehouse also allows the organisation to organise its data, coordinate updates, and see relationships between information gathered from different parts of the organization.