Both mapper classes share a common abstract class. Both are fed from a command table that describes mapping based on transaction types. This makes it possible to add new transaction without code changes. Just update a table.

A key concept, don't change the code to make new transactions work.

This has really worked well, later in the year I watched a programming team integrate a new transactions, it took more time to load and validate the stored procedures than it took to make the table change and notify the visualworks image.