Shrunken Rollup Changing Dimension
Ch.02: DWH | DWH Components | Data Modeling | Dimension Types
Lesson Notes
Shrunken Rollup Changing Dimension Lesson Notes:
Video
Shrunken Rollup Dimensions
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Shrunken Rollup dimension is used for developing aggregate (higher level of summary) fact tables.
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It required that the data model has a lower level of granularity.
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We have a daily usage fact table, and we need to have a higher level of monthly usage. So, we use the monthly dimension to get a summary of the daily.
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We have a daily usage fact table aggregated on area-id, and we need to create another summary table aggregated based on city id. So, the new grain level here is the new dimension for the city.
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Shrunken Rollup Dimensions Cont.
In this example we use the AreaId and the relation with CityID for shrunken the dimension and do higher level of aggregations.
- Order detail per AreaID
OrderDate AreaID TotalOrders 123456789 123 20 123456789 123 30 123456789 678 10 123456789 678 12 - City and Area relationship dimension
AreaID AreaName CityID 123 Al-Matareya 1 678 Ain shams 1 - City dimension
CityID CityName 1 Cairo - Order detail per CityID
OrderDate CityID TotalOrders 123456789 1 72