Measure Types
- Additive - Measures that can be added across any dimensions.
- Non Additive - Measures that cannot be added across any dimension.
- Semi Additive - Measures that can be added across some dimensions.
A fact table might contain either detail level facts or facts that have been aggregated (fact tables that contain aggregated facts are often instead called summary tables).
Special care must be taken when handling ratios and percentage. One good design rule is to never store percentages or ratios in fact tables but only calculate these in the data access tool. Thus only store the numerator and denominator in the fact table, which then can be aggregated and the aggregated stored values can then be used for calculating the ratio or percentage in the data access tool.
In the real world, it is possible to have a fact table that contains no measures or facts. These tables are called "factless fact tables", or "junction tables".
The "Factless fact tables" can for example be used for modeling many-to-many relationships or capture events.
Read more about this topic: Fact Table
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