The rule engine distinguishes two kinds of events, which are managed in two separate event entry queues:
External events. These are events obtained from the Database Event Channel (pulled out of the Business Process Server database event queue by BPM Events using the DEC adapter), events generated by the scheduler, or events coming from JMS queues.
Internal events. These are events generated by BPM Events rules, with the generate() action statement. Note that scheduled events are not considered internal events, even if the scheduler is managed by BPM Events. This is because scheduled events are fired and posted independently from the actual rule processing: the scheduling service could as well be managed outside BPM Events.
Both types of events are treated similarly with regard to rules, but with different priorities: internal events are always processed in higher priority, that is, as long as there are events in the internal events entry queue, the rule engine processes these first. Only when the internal queue is empty, the rule engine processes the next event in the external event queue.
External events. These are events obtained from the Database Event Channel (pulled out of the Business Process Server database event queue by BPM Events using the DEC adapter), events generated by the scheduler, or events coming from JMS queues.