Adding Service Methods to an Application Module
Service methods are methods that are specific to an application module. These methods may be independent of any view in the application. For example, you may need a method that determines the number of current orders for a specific item in inventory. That method can be used from any client without needing to instantiate an inventory or order view.
You can also add code that affects the behavior of a particular view object in the application module; for example, you can change the WHERE or ORDER BY clause of a view object. You would do this if you were reusing a view object in multiple application modules and wanted the view object to behave differently in different application modules.