Right. But Neil explained it in a way that this idiot could understand:
1. Click on a blank space in your composite dw. Such that, you are not selecting any child dw or any object there. Then you will see the Retrieval Arguments for the composite in the Properties pane. You need to define all the arguments for all the child dw's there. In your example, you will need to define the sp_id, company and payment_date.
