A data warehouse is a repository of an organization's electronically stored data. Data warehouses are designed to facilitate reporting and analysisInmon, W.H. Tech Topic: What is a Data Warehouse? Prism Solutions. Volume 1. 1995..

This classic definition of the data warehouse focuses on data storage. However, the means to retrieve and analyze data, to extract, transform and load data, and to manage the data dictionary are also considered essential components of a data warehousing system. Many references to data warehousing use this broader context. Thus, an expanded definition for data warehousing includes business intelligence tools, tools to extract, transform, and load data into the repository, and tools to manage and retrieve metadata.

In contrast to data warehouses are operational systems which perform day-to-day transaction processing.

Benefits of data warehousing

Some of the benefits that a data warehouse provides are as follows: Yang, Jun. WareHouse Information Prototype at Stanford (WHIPS). 1. Stanford University. July 7 1998.Caldeira, C. "Data Warehousing - Conceitos e Modelos". Edições Sílabo. 2008. ISBN 978-972-618-479-9

• A data warehouse provides a common data model for all data of interest regardless of the data's source. This makes it easier to report and analyze information than it would be if multiple data models were used to retrieve information such as sales invoices, order receipts, general ledger charges, etc.
• Prior to loading data into the data warehouse, inconsistencies are identified and resolved. This greatly simplifies reporting and analysis.
• Information in the data warehouse is under the control of data warehouse users so that, even if the source system data is purged over time, the information in the warehouse can be stored safely for extended periods of time.
• Because they are separate from operational systems, data warehouses provide retrieval of data without slowing down operational systems.
• Data warehouses can work in conjunction with and, hence, enhance the value of operational business applications, notably customer relationship management (CRM) systems.
• Data warehouses facilitate decision support system applications such as trend reports (e.g., the items with the most sales in a particular area within the last two years), exception reports, and reports that show actual performance versus goals.

Data warehouse architecture

Architecture, in the context of an organization's data warehousing efforts, is a conceptualization of how the data warehouse is built. There is no right or wrong architecture. The worthiness of the architecture can be judged in how the conceptualization aids in the building, maintenance, and usage of the data warehouse.