Methods, computer systems and apparatus, including computer program products, for handling events in an event-driven software application. An event request specifying an event and values for one or more event parameters is received in a system event handler. The system event handler identifies an action associated with the specified event. The action specifies a required set of parameters and an event handling function specifying one or more operations that can be performed on data. The system event handler generates an instance of the identified action by mapping the event parameter values to the required set of parameters. The event handling function is called in an application event handler with the generated instance of the identified action to invoke application code.