A data mart is a simple form of a data warehouse that is focused on a single subject such as Sales, Finance and Marketing. Given their single-subject focus, Data marts are generally used to draw data from only a few sources. The sources could be internal operational systems, a central data warehouse, or external data. A data warehouse is unlike a data mart, deals with multiple subject areas and is typically implemented and controlled by a central organizational unit, it is called a central or enterprise data warehouse. This basic definition limits the size of a data mart or the complexity of the decision-support data.