Data warehouses consist of relational databases that are programmed to provide responses to user queries. A data warehouses allows for the collection of data from a variety of sources into one location, and usually consists of historical or transaction information.
Data warehouses are subject-oriented, which means that the data collected is all connected along a common subject line. For example, a sales data warehouse would contain all of the sales data available for a company. Because it is a relational database, users can then query the data warehouse, asking questions such as "What is the leading sales product?" The warehouse would then search its database and provide the answer based on the data collected by the system. To be effective, a data warehouse also has to keep the data closely integrated, formatting data in the same way so that it can be easily searched. Data should also be non-volatile, remaining stable and unchanging once placed into the database.
Data warehouses are normally used by managers as a decision-making aid. By collecting the data in a single database, managers can easily refer to the data when making new budgets, determining profitability of products, checking on inventory amounts or anything else that the data in the warehouse is programmed to provide.