This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
What kind of trigger are you talking about? The word is mostly used in conjunction with databases, where triggers are executed in response to DB events like inserts, updates, deletes etc. So the trigger is called by the DB, not by any client application. Maybe if you posted some information about what you're actually trying to accomplish, a more informative answer could be given.