a group of records in a fact table which logically belong together. By including a data set dimension, performance data managers can load data for different versions, realities, assumptions or scenarios in the same table. Likewise, data sets can be used to distinguish between measured values (indicators) and targets.
ICAO (2009), doc. 9883, Manual on Global Performance of the Air Navigation System
Data cannot and should not be aggregated over data sets, but the data sets can be compared against each other: for example, different forecast scenarios, or different forecast editions, or measured values against targets. The data set dimension is an important instrument for performance evaluation. (same source)