Thursday, 13 September 2012

SCD Type 3,Slowly Changing Dimension Use,Example,Advantage,Disadvantage

In Type 3 Slowly Changing Dimension, there will be two columns to indicate the particular attribute of interest, one indicating the original value, and one indicating the current value. There will also be a column that indicates when the current value becomes active.
In our example, recall we originally have the following table:

Customer Key
Name
State
1001
Williams
New York

To accommodate Type 3 Slowly Changing Dimension, we will now have the following columns:
  • Customer Key
  • Name
  • Original State
  • Current State
  • Effective Date
After Williams moved from New York to Los Angeles, the original information gets updated, and we have the following table (assuming the effective date of change is February 20, 2010):

Customer Key
Name
Original State
Current State
Effective Date
1001
Williams
New York
Los Angeles
20-FEB-2010

Advantages
  • This does not increase the size of the table, since new information is updated.
  • This allows us to keep some part of history.
Disadvantages
  • Type 3 will not be able to keep all history where an attribute is changed more than once. For example, if Williams later moves to Texas on December 15, 2003, the Los Angeles information will be lost.
Usage
Type 3 is rarely used in actual practice.

When to use Type 3
Type III slowly changing dimension should only be used when it is necessary for the data warehouse to track historical changes, and when such changes will only occur for a finite number of time.

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