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Monday, December 11, 2017

Slowly Changing Dimensions

Slowly changing dimensions are the dimensions in which the data changes slowly, rather than changing regularly on a time basis.

For example, you may have a customer dimension in a retail domain. Let say the customer is in India and every month he does some shopping. Now creating the sales report for the customers is easy. Now assume that the customer is transferred to United States and he does shopping there. How to record such a change in your customer dimension?

You could sum or average the sales done by the customers. In this case you won't get the exact comparison of the sales done by the customers. As the customer salary is increased after the transfer, he/she might do more shopping in United States compared to in India. If you sum the total sales, then the sales done by the customer might look stronger even if it is good. You can create a second customer record and treat the transferred customer as the new customer. However this will create problems too.

Handling these issues involves SCD management methodologies which referred to as below

  1. SCD Type 1
  2. SCD Type 2
  3. SCD Type 3
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