To facilitate complex analyses and visualization, the data in a
warehouse is typically modeled multidimensional. For
example, in a sales data warehouse, time of sale, sales district,
salesperson, and product might be some of the dimensions
of interest. Often, these dimensions are hierarchical; time of
sale may be organized as a day-month-quarter-year hierarchy,
product as a product-category-industry hierarchy. Typical
OLAP operations include rollup (increasing the level of
aggregation) and drill-down (decreasing the level of
aggregation or increasing detail) along one or more
dimension hierarchies, slice_and_dice (selection and
projection), and pivot (re-orienting the multidimensional view
of data).