Datawarehousing

Bridge Tables Implement Data Mart Hierarchies

The bridge table supports a many to many relationship between facts and dimensions.  For example, a bridge table could show the percentage commission split between multiple sales reps (dimension) and a sale (fact).

Data Modeling Slowly Changing Dimensions

At times, dimension data must change and that must be handled in the data mart.  Ralph Kimball has identified the following slowly changing dimension (SCD) types that are widely recognized in data mart design:

 

SCD Type 1

Data is overwritten and prior data is not retained.

SCD Type 2

A new row with the changed data.

SCD Type 3

Update attributes with in the dimension row.  For example, we could maintain both current customer status code and prior customer status code.