You can use the Group functionality in Web Intelligence to group values returned by an object into categories. These categories can then be used as the basis for aggregating measures at higher levels.

For example, the eFashion.unx universe contains Quarter and Quantity sold objects, which allow you to analyze the quantity sold totals for each quarter. However, if your reporting requirement is to display the quantity sold measure aggregated at the half-year of details, then the universe does not provide the objects that you need to meet this requirement.
By creating a Half Year variable based on the Quarter object, you can aggregate quantity sold totals for each half of the year. This data can then be presented in the same report with sold totals for each quarter.