BPM Engine vs BPM Engine Server

Question

I'm doing some research on the workflow concepts and specifically BPMN standard. And I'm mostly interested in the available software on the subject.

I've already studied software like Activiti and jBPM, both of which are implemented in Java. As great as they are, I'm looking for something else. Even though such software call themselves BPM Engine I would rather name them BPM Engine Servers. They are stand alone servers (with web based GUI) which makes it really hard to embed them in other servers.

Now my question is: Is there a concept as BPM Engine in the manner it only executes the given BPM with the given data, only one step? Without any GUI or direct user interaction (something like a library)? What should I search for? What is it named? Are my expectations valid?

[UPDATE]

I've spent the last hours studying Activiti's user guide. I'm still not sure if I can use it the way I want it to! And I'll be grateful if someone can confirm it.

I'm interested in a console-like application which I can run whenever I like, give it the previously running process (most likely serialized as a string). The engine should construct the process based on the given history.

Once the process is reconstructed, I would like to move it forward one step by telling it what has happened. Then it should inform me of the next tasks to be performed and shutdown.

Finally I'll be storing the updated process after getting it as a string (the engine should serialize it in a way so it can unserialize it later).

I don't want the engine to have its own database or memory storage. I want it to shutdown completely once it's done. This is what I mean by Engine, no user interaction, no storage access.

Can any of the BPM engines perform in such a way?

Answer 1

perhaps I am missing your point, but Activiti is really nothing more than a jar file that can be embedded in any other java application. Certainly in order to run Activiti in any meaningful way you need a backing datastore (database) and one or more process definition, but as you can see from the unit tests that are part of Activiti, the database can be in memory and the process definition can be included in the war. There are many examples of Activiti (and likely jBPM) used as simply an embedded state machine with no exposed UI or user interaction. My company has implemented a number of such solutions for different organizations. If I have missed your point, feel free to give me an example of your requirement, I'm sure we have addressed it at one time or another.

Answer 2

You might be interested in Bonita BPM. This open source BPM solution offers an execution engine that can be used as a standalone. Just like its competitors, it also offers an optional GUI in the form of a web based application: Bonita Portal.

Answer 3

I think the challenge for what you want to do is that most of the BPM Engines separate the definition of the process from the execution. So for most of them you need someplace that will allow you to store the definition long term (typically a database) and then they track the state of a given instance of that definition for you.

If you wanted a truly stateless BPMN "interpretation" engine, then your serialized data would have to include not only the current state of the process, but he process definition as well. I'm sure this can be done, but I don't think any of the engines have taken this approach as doing so would add complexity to the solution, and solves a problem that not many people seem to be asking about.

Additionally it begs the question "given that we now have a process that knows what task it is on, how does that task actually get executed?" In most of the solutions I've seen the execution of the task takes place in the same server as the engine. In some where the execution is in a different technology, the "executor" doesn't understand the Process much at all except to make a call to signal "okay this thing is done" and the engine handles what happens next. You want to have this data in a serialize data structure of some sort, so the question would arise "If we have this stateless BPMN Engine, would the executor of the task have to update the serialized data to indicate the state change for the task".

There are other requirements of the BPMN specification that I think would make your approach very difficult, such as how to handle items like Intermediate Message Events that are either waiting for a specific time, or a message, before moving the process forward. While all of these are potentially solvable, it certainly would take significant re-engineering of current approaches.