Slowly Changing Dimensions — SCD

Slowly Changing Dimension:-

For an ETL developer this is must to know that it is possible that the dimension might changes over time, like wise a product may changes his price and a customer changes his contact information, some of the changes are needed to be recorded and some of them may not, to track these changes  a technique used called Slowly Changing Dimensions(SCDs)

Reason to Model SCDs

If a product price changes over time we will lost the previous one that would result in the stats that the prices is remain same.

Incremental Update using Pentaho Kettle

Incremental update (SCD Type 1, Type 2 or Type 3) is the most corner stone developing ETL scripts for populating a Data mart.

Pentaho Kettle is a marvelous tool for data migration in very easy steps. I have been using Kettle for multiple Business Intelligence projects for data migration purpose and I found it very easy to learn and produce the desired out put with in no time. Kettle provides a very useful step Dimension Lookup-Update for incremental update your dimensions. Read full story »

Slowly Changing Dimension (SCD) Types

SCD Types

In his book The Data Warehouse Toolkit, Ralph Kimball brought us the idea of slowly changing dimensions. In fact he defined three types of slowly changing dimensions – called Type 1, Type 2, and Type 3.

Type 1
The Type 1 slowly changing dimension is simply overwriting the row in the dimension with the new data. There is no history kept. Doesn’t that defeat the purpose of a subject-oriented, time variant, integrated,non-volatile data store? Yes, it does, but it is also the easiest type to implement and uses the least amount of storage. After all, we areused to reading rows and updating them – that is what transaction systems are all about. Read full story »

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