Slowly Changing Dimension
A dimension that has level or attribute data that needs to be updated.
Data changes in the fields for levels or attributes is one of the most challenging design issues for multidimensional (star schema) data modeling. This issue is often referred to as the handling of Slowly Changing Dimensions. There are three ways outlined by Ralph Kimball (and others) to handle this situation:
Type #1. Change the data in the dimension table.
Type #2. Add new records to the dimension table that contain the new data.
Type #3. Add new fields to the dimension table to contain the values before and after the change.
Various authors (including Ralph Kimball) also suggest the splitting of dimensions into separate dimensions when a consolidated dimension would result in a high level of dimension change.