Dimensional Modeling - Slowly Changing Dimensions
* Type 1 - Overwrite Original Value
A change does not require tracking
* Type 2 - Add a new record
With Type II SCD, a new version of the dimension record (row) is created, and the existing version is marked as history.
Each row does not correspond to a different instance of an entity but a different “state”, a “snapshot” of the instance at a point in time.
Note: Tracking changes in dimension is referred in datawarehousing as slowly changing dimensions.
In the source system a lot of changes are daily made :
new customers are added,
addresses are modified,
new regional hierarchies are implemented,
or simply the product descriptions and packaging change.
These sorts of changes need to be reflected in the dimension tables and in several cases, the history of the changes also needs to be tracked.
By remembering history, we are then able to look at historical data and compare it to their current situation.
