Implementing custom rollups using MDX formulas

The reporting dimension created in the previous recipe is not connected to any measure group. That means it can't be used to display meaningful data. Yet.

Welcome custom rollups using MDX formulas!

Custom rollups are a way to tell dimension members what data to show. They are in fact MDX expressions that return a value. That value is displayed as the value of a member in the dimension. Each member can have its own expression, its own custom rollup. This expression, stored in a column in the relational table or a view, can be specified as the value of a certain property of any parent-child dimension. However, that only works when the dimension has a relationship with a fact table, with a measure group. In our case, it is not so. Our reporting dimension is completely loose, it can have any item as long as it has a formula for it. This flexibility comes at a price. We can't use the pre-build functionality of custom rollups, we have to invent our...