Subject-oriented means the data warehouse focuses on the high level entities of the business. Integration means the data is stored in consistent format. It is extremely different in content and technical requirements from transactional systems. It is in this context that data warehousing will be examined. The data is integrated and transformed before being loaded into the data warehouse.
Users access the data warehouse by using a front-end tool or application.
Data is made readily accessible without interrupting on-line operational workloads. System design is much simpler with one data source. There is no need to perform query optimization over heterogeneous sources, and since query execution does not involve data translation and communication with remote sources, complex queries can be executed easily and more efficiently. Analytical applications are much easier to implement and use when data is consolidated. A warehouse takes snapshots of operational data over and over again at specific intervals.