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?
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.