What is ETL Mapping Document ?A Real Time Example

One of the regular viewer of this blog requested me to explain the important's of the ETL mapping document.

What is ETL Mapping Document :
                               The ETL mapping document contains the source,target and business rules information's, this document will be the most important document for the ETL developer to design and develop the ETL jobs.

                             A typical mapping document should contain the following information's

1) Mapping indicator(Values A:ADD, D:Delete,C:Change)
2) Change description (Used to indicate mapping changes)
3) Key Indicator( Indicates whether the field is Primary key or not)
4) Source Table/File Name
5) Source Field Name
6) Source Field Data Type
7) Source Field Length
8) Source Field Description(The description will be used as a meta data for end user)
9)Business Rule
10)Target Table Name
11) Target Field Name
12) Target Data Type
13) Target Field Length
14) Comment

You can add more fields based on your requirement.

Real Time Example:
Let's take a look at a real time example here, consider that we are getting a source file called "Employee_info" which contains employee information's and it should get loaded into the EMP_DIM table in target. 

One of the business requirement is to convert Sales -->S,Packing-->P and Transport-->T

Row id	Emp First Name	Emp Last Name	EMP No	EMP Dep
1	John	Beck	2001	Sales
2	Mike	Morry	2002	Sales
3	Kevin	Peter	2003	Packing
4	Steve	Morry	2004	Packing
5	Jim	Chen	2005	Transport

Here is how the mapping will look like

Once the mapping is prepared, it needs to be reviewed with end user and get the sign off from the them.

Lets say that during the review they users want to add "E" before the EMP_NUM field in target.
The mapping document should be changed first, here it's how it will look after the change

 As you can see in the image that the "Mapping Indicator" column got changed from A to C and "Change description" contains change details.