A calculated member is a dimension member whose value is calculated at run time using an expression that you specify when you define the calculated member. Calculated members can also be defined as measures. Only the definitions for calculated members are stored; values are calculated in memory when needed to answer a query.
Calculated members enable you to add members and measures to a cube without increasing its size. Although calculated members must be based on a cube’s existing data (such as members), you can create complex expressions by combining this data with arithmetic operators, numbers, and a variety of functions. Microsoft® SQL Server™ OLAP Services not only includes a library of over 100 functions but also allows you to register and use other function libraries.
For example, suppose executives in a shipping company want to determine which types of cargo are more profitable to carry, based on profit per unit of volume. They use a Shipments cube containing the dimensions Cargo, Fleet, and Time and the measures Price_to_Ship, Cost_to_Ship, and Volume_in_Cubic_Meters; however, the cube does not contain a measure for profitability. You can create a calculated member as a measure named Profit_per_Cubic_Meter in the cube using the existing measures in the expression:
([Measures].[Price_to_Ship] - [Measures].[Cost_to_Ship]) / [Measures].[Volume_in_Cubic_Meters]
The next time the Shipments cube is browsed, Profit_per_Cubic_Meter appears along with the other measures.
For more information, see Creating Calculated Members and Calculated Member Builder.