multidimensional databases

Multidimensional databases, such as OLAP, present data hierarchically by using cubes, dimensions and elements. A cube is a collection of dimensions which contain a number of elements. You may have, for example, a Sales cube containing a Product dimension containing individual product elements; a Time dimension containing years as its elements, and a Region dimension containing countries. These hierarchical structures are difficult to represent efficiently in SQL. Multidimensional databases are particularly useful where the data has a Time dimension and so are often used in planning applications.