Directly Executing BPMN

The article “Why BPEL is not the holy grail for BPM” presents a scenario for implementation which is difficult for BPEL based products to actually execute. It presented a particular product based on BPEL that was not able to execute this diagram.  What about products that are based on executing the BPMN directly without conversion?

Fujitsu Interstage BPM is such a product. You draw the BPMN diagram, and submit the diagram to the server, and the server executes it directly. It has no problem executing the diagram as drawn. Here is the diagram as drawn in the Fujitsu Studio:

Some slight modifications: Instead of an “activity” receiving the start message, I use a start-event which receives the message. I don’t understand why people draw processes that start and then immediately go to an activity that waits for something — a start event does this much more clearly. There are many who feel that waiting for a message should always be done by an event node, and never an activity node, and that certainly seems to make sense to me. Using the start node to be triggered by the incoming message is the same semantics. Similarly, the original diagram had a final activity which was not really an activity, but really only an indication of the final state, and I would use an exit node (end event) to indicate that. But the real question was with the middle section and that is reproduced faithfully.

This is saved as XPDL. I do not say that this is transformed to XPDL, because there is no transformation. The diagram above is expressed directly, one-for-one, into XPDL which is simply a file format for storing BPMN diagrams. When you read the XPDL back in, the same BPMN diagram as you see above is displayed. XPDL is simply used as a file format to transfer BPMN diagrams around. The XPDL file is imported into the server through a web form:

Then in the server the process definition is displayed as BPMN using the Flash based process diagram viewer:

Then we start an instance of the process.  Since two activities are started in parallel, you will have two workitems in the worklist.

Step 1

The worklist has two workitem on it, “Provide Office” and “Fill HR DB”:

And this can be visualized graphically as:

Because these steps are in parallel, they could be completed in either order. To demonstrate how the AND node holds up the progress until both inputs are received, lets complete the “Provide Office” first.

Step 2

One work item available:

And this can be visualized graphically as:

The the “Fill HR DB” has not been completed, and so that task is still on the list. The Provide Computer step can not be started before the Fill HR DB step is completed, because the AND node requires input from both direction.  There is only one active activity (indicated with green) and so we have one workitem.  The AND node is colored green here to show that it has received one, but not both inputs.  We complete the “Fill HR DB” workitem:

Step 3

This has two workitems available again:

And this can be visualized as:

Completing the “Fill HR DB” sent an event to the “Medical Check” activity to activate it, as well as to the AND node, satisfying that, and causing “Provide Computer” to be activated as well.  So we have two activities active at this time.  Again, these are in parallel, and so they could be completed in either order, so lets choose to complete the “Medical Check” workitem.

Step 4

We are left with only one work item:

And this can be visualized as:

So now we complete that one remaining workitem

Step 5

Now we have completed the process, there are no workitems:

And this can be visualized as:

Summary

So you see, the BPMN can be executed directly.  There is no need to translate into any other form. The process is transferred to the server as a BPMN diagram, using XPDL as a file format. The diagram is interpreted directly without conversion to another model. You can execute diagrams that are not possible with BPEL. And the advantage is that you can directly see how the process is running.

Why again do analysts recommend BPEL?  It seems to me in this scenario to be nothing but a limitation.