In the past, I've created custom SQL operations, but now I had something trivial to do, so I decided to take EnsLib.SQL.Operation.GenericOperation out for a spin. There's no example in the docs, so it was a little tricky. Here's what I ended up doing:
In my external database, I have 'mytable' with two fields 'id1' and 'id2'. Here are the pertinent Business Operation settings:
SQL: select id2 from mytable where id1 = ?
Input Parameters: [1] *id1
RequestClass: Ens.