Decision support applications involve complex queries on very large databases. Since response times should be small, query optimization is critical.
Users typically view the data as multidimensional data cubes.
Each cell of the data cube is a view consisting of an aggregation of interest, like total sales. The values of many of these cells are dependent on the values of other cells in the data cube. A common and powerful query optimization technique is to materialize some or all of these cells rather than compute them from raw data each time. Commercial systems differ mainly in their approach to materializing the data cube. Dimensions, measures and aggregation hierarchies are the core concepts in data warehouses.