| SCD - Type 1 | SCD - Type 2 |
SCD Type 3
In the Type 3 Slowly Changing Dimension only the information about a previous value of a dimension is written into the database. An 'old 'or 'previous' column is created which stores the immediate previous attribute. In Type 3 SCD users are able to describe history immediately and can report both forward and backward from the change.
However, that model can't track all historical changes, such as when a dimension changes twice or more. It would require creating next columns to store historical data and could make the whole data warehouse schema very complex.
To implement SCD Type 3 in Datastage use the same processing as in the SCD-2 example, only changing the destination stages to update the old value with a new one and update the previous value field.
SCD Type 4
The Type 4 SCD idea is to store all historical changes in a separate historical data table for each of the dimensions.
To implement SCD Type 4 in Datastage use the same processing as in the SCD-2 example, only changing the destination stages to insert an old value into the destionation stage connected to the historical data table (D_CUSTOMER_HIST for example) and update the old value with a new one.