How Database Events Are Handled
4GL database event statements allow an application to notify other applications that a specific event has occurred. The other application then can use that information to perform some action that you designate.
The sequence for handling a database event is:
1. A sending application or database procedure raises the event.
2. The Ingres DBMS Server notifies other applications, called receiving applications, that the event has occurred.
3. A receiving application takes some action based upon the event. (The receiving application can be the same as the sending application.) The receiving application must:
• Be registered to receive notification when the event is raised
The server performs this notification by placing the event into an event queue within the receiving application.
• Extract the event from the queue
• Retrieve any desired information about the event
You can designate any program code within an application as a database event. For example, within an inventory control application, you can raise an event when an update causes the supply of a part to fall below a specified amount. A second application then is notified to reorder the part.