Earlier in my blog, Slowly Changing Dimensions – Special Attention Needed, I touched upon the need to pay special attention to slowly changing dimensions. Organizations have three variants of implementing solutions for slowly changing dimensions.

Type 1: in these implementations, the latest data is retained. This is implemented when there would be no need to do historic analysis. For example, an online transactional system that needs to display the latest list of values in the pull-down pick lists may use this type.

Type 2: in these implementations the history or the validity period for the changes is persisted.

Margaret, who was an average sales person, moved from Washington, DC to Richmond, VA, whose market is one fifth the size, during the month of June.  When the annual evaluations of sales performance were done in the month of December, she was listed as the top performer in the Richmond market resulting in the company promoting her to Sales Director.  The next two highest ranked Richmond salespeople had been the consistent leaders for the last several years and outperformed Margaret since she arrived in Richmond.  Her very high sales numbers during the first six months of the year skewed her average, placing her above the rest of the Richmond area.  In this example, if the decision makers had correct information handy, and used it appropriately, would they have promoted Margaret over her new Richmond peers?

Here is another example.