The write-back feature allows data analysts to perform what-if analysis and is typically used for budgeting applications. For example, an operations manager might want to see what the profit margins would look like if her team were to achieve a cost reduction of 10 percent. Although not frequently used, write-back is a useful feature.
Analysis Services does not overwrite any values in the existing fact tables from which it sources data. Rather, it creates a new partition for storing the write-back data. The new partition is based on a table that could be stored in the same database as the primary fact table or in a different relational database. SSAS derives requested values at the query execution time by aggregating write-back and regular partition values. Note that the write-back feature works only on measure groups that have measures using the SUM
aggregation function. If you have followed along with the examples in this chapter, you must remove the Fact Reseller...