Shrunken rollup dimensions

S**hrunken dimensionsare conformed dimensions that are a subsetof rows and /or columns of a base dimension. Shrunken rollupdimensions are required when constructing aggregate fact tables. They are also necessary for business processes that naturally capture data at a higher level of granularity, such as a forecast by month and brand (instead of the more atomic date and product associated with sales data). Another case of conformed dimension subsetting occurs when two dimensions are at the same level of detail, but one represents only a subset of rows.