Key Performance Indicator (KPI) fact tables share a lot of similarities with the rollup fact tables in that they are typically at a monthly level of granularity and they combine information from multiple detail fact tables. They differ in that they provide specific sets of pre-defined information (KPIs). Such KPIs are often difficult to answer and require the implementation of some form of business rule. Also they often provide pre-calculated year-to-date, same month last year, and previous year-to-date values for easier comparisons. They have a KPI dimension which provides a list of all the specific statistics or performance indicators we are tracking.
An example from our previous sales examples may be a set of KPIs dealing with customer acquisition and loss. We may have a specific KPI that records the number of new customers during the period and the $value of their business during that period. Another KPI may record the percentage growth of all customers over the last six months. Another may show the number of customers who closed their accounts in the period, and the value of their business over the preceding 12 months.
KPI fact tables require the specific definition of each KPI.