iSeries/ AS400/ System i programming allows a very useful feature called Triggers. It allows you to execute programs based on data changes in a database file. Use the command ADDPFTRG to add triggers to any database file. Recently, I used trigger to create a history/ audit trail for a Client Locations file which does not have any history. Trigger was preferred over direct program changes because One small program does the job well. Least impact and least testing involved! It saves me time and effort having to add code in a dozen places. It saves on testing time because of large number of changes. The performance overhead is negligible. Follow this link to a useful article on Trigger programming http://www.tylogix.com/Articles/TriggerTechniquesRevisited.htm .
Senior Analyst Programmer with 17 years of experience on AS400.