Slowly Changing Dimensions
Slowly Changing Dimensions are a recurring topic in Business Intelligence and Data Warehousing in general. Theterm describes the unpredictable change of dimensions over the life-cycle of a data model and the approachesused to capture and document historical data for future reference.
Before:
After:
There are 4 ways to deal with them:
Dimension Update
Parallel Hierarchies
Split information over different dimensions
Attribute/Control Cube
Dimension Update (Slowly Changing Dimensions)
The first approach is the so-called “Update” approach. As the word “Update” suggests, this approach removes theold structure and replaces it with the new one. This approach has proven to be efficient, in the case when no historicalcomparison is required. The latest structural changes should simply be displayed in the respective dimension.
Parallel Hierarchies (Slowly Changing Dimensions)
An approach to preserve historical structures and information is to create so-called “parallel hierarchies”. Herebythe new structure is created under a new consolidated element in the respective dimension.Attention should be paid to how many parallel hierarchies are being set up as this method can quickly “clog” thedimensions...