Creating a flow service that matches references and values

Hello, i’m new at wm ESB, i want to develop a flow service that takes as input two files : the first File1 containing the references between An and Bn and the second File2 the value corresponding to the reference (i.e A1->B1 for the value 2 ).

And as output i want to have the File1 but with references replaced by values.
Any idea or any tip?