If you declare mapping parameters and variables in a mapping, you can reuse a mapping by altering the parameter or variable values of the mapping in the session. Reuse a mapping to reduce the overhead of creating multiple mappings when only certain attributes of a mapping need to be changed.

When you use a mapping parameter or variable in a mapping, you first declare the mapping parameter or variable for use in each mapplet or mapping. Then, you define a value for the mapping parameter or variable before you run the session.

You can declare mapping parameters with the same name for use in a mapplet and a mapping. If the mapping parameter in a mapplet does not have a value, the parameter takes the value of the mapping parameter with the same name in the mapping.

Use mapping parameters and variables in a mapping to incrementally extract data. Use mapping parameters or variables in the source filter of a Source Qualifier transformation to determine the beginning time stamp and end time stamp for incrementally extracting data.

For example, you can create a user-defined mapping variable $$LastUpdateDateTime to save the time stamp of the last row that the Integration Service read in the previous session. In the source filter, use $$LastUpdateDateTime for the beginning time stamp and the built-in variable $$$SessStartTime for the end time stamp. Use the following filter to incrementally extract data based on the SALES.sales_datetime column in the source: