topic Re: Process Event Bus in Activiti Engine in Alfresco Archive

Process Event Bus in Activiti Engine

cstettler — Fri, 20 Aug 2010 13:59:56 GMT

Dear Activiti community,I'd like to get your feedback on the idea of having a process event bus component as part of the Activiti engine. The process event bus is a lightweight and extensible "message bus" that allows for registering to and receiving events with rich context information from the Act

Re: Process Event Bus in Activiti Engine

micha_kiener — Fri, 20 Aug 2010 14:17:17 GMT

As we want Activiti being adopted not only by developers, but also by BPM product vendors, ISVs and others, the Process Event Bus is a great mechanism for loosely coupled extensions to the engine.

Even in a project scenario where specific requirements are needed, the PEB supports an easy way of extending the core functionality given by the Activiti engine.

As an addition, we used the PEB for runtime SLA management, whereas we tracked the generation of process instances and task creation / completion using events on the bus and calculated the time they used in comparison with the SLA agreed with the customer. That could be done totally loosely coupled from the engine in a generic way.

Re: Process Event Bus in Activiti Engine

trademak — Fri, 20 Aug 2010 20:18:40 GMT

I really like the idea of the process event bus.
A high-class BPM engine should have a solid and clear way of handling events and this is a good solution.
I think it would also be nice if you can fire custom events and specific points in a BPMN proces.
This can then be used to create all kinds of process reports.
It would also be nice if process variables can be part of the event message.

Best regards,

Tijs

Re: Process Event Bus in Activiti Engine

tombaeyens — Mon, 23 Aug 2010 07:08:45 GMT

I'm mostly interested to know the concrete use cases for which this generic mechanism is necessary.

Currently in the process execution, we have static events being fired to avoid lots of unnecessary object creation. But this means that the event mechanism has to be process execution aware. Because we pass the execution as a parameter to the listener. So in the current event mechanism, listeners can access the process variables because they have access to the execution. And if you don't access the variables, they are not loaded from the db.

In Micha's proposal, the difference is that the event listener mechanism is more generic (like e.g. the java util listener). So that it can also be used for other situations then only for process execution.

In the approach that I take, we build specific listeners for each purpose and that way, the event names can be static. And the context can be derived from the specific object like execution or task.

If companies want to add a generic layer, then that should be possible. In that case, the generic process event bus could listen to e.g. all process execution events, all task events and maybe even more events. Then a full event object could be instantiated and dispatched in the generic process event bus. But imo, the instantiation of these event objects and the generic event bus should be optional. As for now, I don't see the use cases that mandate or justify such a generic approach.

Re: Process Event Bus in Activiti Engine

kurt — Tue, 24 Aug 2010 06:48:47 GMT

Process Event Bus - the real innovation of Activiti

I have build a rule based process engine and i have implemented such an event bus - but I didn´t call it PEB.
Following features could integrated in a proper way:
- logging of all engine events
- visualization of rule / process engine states with SVG
- integration of application specific task assignment implementation
- debugging support of the engine
- …..

For my opinion, the PEB is the key feature for lightweight process engine and für powerfull adaptability!

"unnecessary object creation"
if no event listener is registered, no event object must be created.

"If companies want to add a generic layer, then that should be possible"
In real world situations most of companies will really need this generic event mechanism.

Best regards

Kurt

Re: Process Event Bus in Activiti Engine

cmuelder — Tue, 24 Aug 2010 07:01:39 GMT

hi tom,

from our point of view regarding the main business processes for data exchange in the utilities market, there are always additional things that have to be done. E.g. if we receive mails to start a process, this mail needs to be copied to other folders or send to other people. If a process instance is finished, i could trigger the archiving of the relevant data.

These "activities" might be interesting, but i don´t want to model those for our main business processes.

Re: Process Event Bus in Activiti Engine

tombaeyens — Tue, 24 Aug 2010 07:10:35 GMT

Christian, how do you want to subscribe to those events then? In the process definition? or in the Activiti Engine configuration? or does this question miss your point?