Using Reference No. in Functions 
You can use reference numbers to refer to source nodes in functions.
You can drag source nodes to functions used as arguments in expressions of Condition or to the Function pane in expressions of Value.
Right-click a target node and choose Mapping Setting.
The Mapping Setting tab opens.
To use reference numbers in arguments of expressions, do the following:
Select the type as Function.
Specify the function and leave blank the parameter for which you want to use a reference no.
Press the Ctrl key and drag the source node to the blank that you saved for the reference no. in the function.
To use a reference number in Function, press the Ctrl key and drag the source node to Function.
You can use a reference number for functions used as customized validation parameters.
Select the target node and select the Validation tab.
Select the customized validation parameter.
In the expression, for the argument in which you want to use a reference number, select the type as Function.
In the argument, specify the function and leave the parameter that you want to use reference number blank.
Press the Ctrl key and drag the source node to the blank that you saved for the reference number in the function.