Data Warehousing provides an effective approach to deal with complex decision support queries over data from multiple sites. Data warehousing is used for analyzing data stored in data warehouses, are rooted in database management systems and artificial intelligence. Data warehousing is integration of data, integration of data with knowledge and integration of various methods applied on the data for analysis. Data warehousing facilitates analysis of stored data and effectively handles on-line analytical processing for decision support queries in many business applications. This serves as an enabling technique of data mining, an integration of OLAP and data mining. Data warehousing deals with the process of constructing and using data warehouses.