SCD Type 2 implementation in Informatica 

Dimensions that change over time are called Slowly Changing Dimensions. For instance, a product price changes over time; People change their names for some reason; Country and State names may change over time. These are a few examples of Slowly Changing Dimensions since some changes are happening to them over a period of time.

SCD type 2 will store the entire history in the dimension table.

We will see how to implement the SCD Type 2 Flag in informatica. As an example consider the customer dimension. The source and target table structures are shown below:

Source table--> Customer

Customer_Id

Location




Target dimension table --> Customer_Dim

Cust_Key_Number

Customer_Id

Location

Flag

The basic steps involved in creating a SCD Type 2 Flagging mapping are

• Identifying the new records and inserting into the dimension table with flag column value as one. Flag column value as 1 correspond to active records
• Identifying the changed record and inserting into the dimension table with flag value as one.
• Identify the changed record and update the existing record in dimension table with flag value as zero. Flag value 0 identifies the record as inactive or historical.

We will divide the steps to implement the SCD type 2 flagging mapping into four parts.

SCD Type 2 Flag implementation - Part 1

Here we will see the basic set up and mapping flow require for SCD type 2 Flagging. The steps involved are:

• Create the source and dimension tables in the database.
• Open the mapping designer tool, source analyzer and either create or import the source definition.
• Go to the Warehouse designer or Target designer and import the target definition.
• Go to the mapping designer tab and create new mapping.
• Drag the source into the mapping.
• Go to the toolbar, Transformation and then Create.
• Select the lookup Transformation, enter a name and click on create. You will get a window as shown in the below image.

• Select the customer dimension table and click on OK.
• Edit the lookup transformation, go to the ports tab and remove unnecessary ports. Just keep only Cust_key, customer_id and location ports in the lookup transformation. Create a new port (IN_Customer_Id) in the lookup transformation. This new port needs to be connected to the customer_id port of the source qualifier transformation.

• Go to the conditions tab of the lookup transformation and enter the condition as Customer_Id = IN_Customer_Id
• Go to the properties tab of the LKP transformation and enter the below query in Lookup SQL Override. Alternatively you can generate the SQL query by connecting the database in the Lookup SQL Override expression editor and then add the WHERE clause.

SELECT  Customers_Dim.Cust_Key as Cust_Key,
        Customers_Dim.Location as Location,
        Customers_Dim.Customer_Id as Customer_Id
FROM    Customers_Dim
WHERE   Customers_Dim.Flag = 1

• Click on Ok in the lookup transformation. Connect the customer_id port of source qualifier transformation to the In_Customer_Id port of the LKP transformation.
• Create an expression transformation with input/output ports as Cust_Key, LKP_Location, Src_Location and output ports as New_Flag, Changed_Flag. Enter the below expressions for output ports.

New_Flag = IIF(ISNULL(Cust_Key), 1,0)
Changed_Flag = IIF( NOT ISNULL(Cust_Key) AND
               LKP_Location != SRC_Location, 1, 0)

• The part of the mapping flow is shown below.

SCD Type 2 Flag implementation - Part 2

In this part, we will identify the new records and insert them into the target with flag value as 1. The steps involved are:

• Now create a filter transformation to identify and insert new record in to the dimension table. Drag the ports of expression transformation (New_Flag) and source qualifier transformation (Customer_Id, Location) into the filter transformation.
• Go the properties tab of filter transformation and enter the filter condition as New_Flag=1
• Now create a update strategy transformation and connect the ports of filter transformation (Customer_Id, Location). Go to the properties tab and enter the update strategy expression as DD_INSERT.
• Now drag the target definition into the mapping and connect the appropriate ports of update strategy transformation to the target definition.
• Create a sequence generator and an expression transformation. Call this expression transformation as "Expr_Flag".
• Drag and connect the NextVal port of sequence generator to the Expression transformation. In the expression transformation create a new output port (Flag) and assign value 1 to it.
• Now connect the ports of expression transformation (Nextval, Flag) to the Target definition ports (Cust_Key, Flag). The part of the mapping flow is shown in the below image.

SCD Type 2 Flag implementation - Part 3

In this part, we will identify the changed records and insert them into the target with flag value as 1. The steps involved are:

• Create a filter transformation. Call this filter transformation as FIL_Changed. This is used to find the changed records. Now drag the ports from expression transformation (changed_flag), source qualifier transformation (customer_id, location), LKP transformation (Cust_Key) into the filter transformation.
• Go to the filter transformation properties and enter the filter condition as changed_flag =1.
• Now create an update strategy transformation and drag the ports of Filter transformation (customer_id, location) into the update strategy transformation. Go to the properties tab and enter the update strategy expression as DD_INSERT.
• Now drag the target definition into the mapping and connect the appropriate ports of update strategy transformation to the target definition.
• Now connect the Next_Val, Flag ports of expression transformation (Expr_Flag created in part 2) to the cust_key, Flag ports of the target definition respectively. The part of the mapping diagram is shown below.

SCD Type 2 Flag implementation - Part 4

In this part, we will update the changed records in the dimension table with flag value as 0.

• Create an expression transformation and drag the Cust_Key port of filter transformation (FIL_Changed created in part 3) into the expression transformation.
• Go to the ports tab of expression transformation and create a new output port (Flag). Assign a value "0" to this Flag port.
• Now create an update strategy transformation and drag the ports of the expression transformation into it. Go to the properties tab and enter the update strategy expression as DD_UPDATE.
• Drag the target definition into the mapping and connect the appropriate ports of update strategy to it. The complete mapping image is shown below.

p