When editing a mapping, you can view source column dependencies for a target column. Viewing source column dependencies lets you see from which source columns a target column receives data.
To view column dependencies, right-click a target column in a mapping and choose Show Field Dependencies. The Designer displays the Field Dependencies dialog box which lists all source columns connected to the target column.
When you define a port expression that performs a calculation using multiple source columns, and then connect that port to a target column, the Field Dependencies dialog box lists all source columns you use in the expression.
For example, you have the following mapping:
Define the following expression in the Q3_sales port in the Aggregator transformation:
LAST(sales, quarter = 3)
Right-click the Q3_sales target column and choose Show Dependencies.
The following figure shows the Field Dependencies dialog box that appears: