A data warehouse (DW) is an integrated repository of data put into a form that can be easily understood, interpreted, and analyzed by the people who need to use it to make decisions. The most widely cited definition of a DW is from Inmon  who states that “a data warehouse is a subject-oriented, integrated, time-variant, and nonvolatile collection of data in support of management’s decisions.”
The subject-oriented property means that the data in a DW are organized around major entities of interests of an organization. Examples of subjects are customers, products, sales, and vendors. This property allows users of a DW to analyze each subject in depth for tactical and strategic decision-making.
The integratedproperty means that the data in a DW are integrated not only from all operational database systems but also some meta-data and other related external data. When data are moved from operational databases to a DW, they are extracted,...