OAF Personalization: making one column value auto-populate depending on another column value chosen

in Self-Service OAF page I need to make the value populate automatically in one field, say field AAA, from a mapping table created when a mapped value is selected in another field, say field BBB,  is chosen. I am looking to do this using OAF personalization but wondering if I could do it without having to go through JDeveloper to change database java objects. If not, is there a document that helps me do this as a bignner/novice?

BTW, I was able to do this in forms personalization adding a query to the item value for the trigger of concern.