Writeback is a feature that allows you to modify OLAP cell values and see the effects ripple through the data set, automatically modifying child and parent cells, and also cells derived using calculations. This allows you to perform 'what if' analysis and applications such as budgeting.
I have added experimental support for writeback to Mondrian.
In Mondrian's case, the term 'writeback' is a bit misleading. In a ROLAP system such as Mondrian, writing back to the database would be difficult, since values are stored in a fact table but we allow cells of any granularity to be modified. One modified cell might contain thousands of fact table rows. So, we don't write cells back to the database, but just retain the modified cells in memory, and propagate the modifications to related cells.
Here's how to use the experimental writeback support. Some of the details may change later as we make the feature more usable.
First, …