In xpdl ,WorkflowProcess is mainly made up of activities and transitions.In my view ,this structure does not describe the nature of the system.

I think that ,a system is composed of two parts,first is the business sub-system, and then the workflow sub-system. When the system run, the "control flow" exchanges between the business sub-system and the workflow sub-system.

For example , after a actor commits a form and completes his work, the workflow sub-system gets the control. It is now the workflow sub-system's duty to determine the next business step.

After the workflow sub-system makes its decision, the business sub-system gets the control,and waits for another actor to join the business.

So, in my view ,the WorkflowProcess is made up of Activities、Synchronizers and Transitions. Activity represents the business logic, the Synchronizer represents the workflow logic, and the Transition represents the control flow. my workflow process diagram is as follows:

It is exactly a Petri net ,isn't it?
By the way, i think that the XPDL is too complex. I have simplified and extended it.
I have provided a designer, a simulator and an open source engine. The attatchment is the picuture of the designer and the workflow process simulator. You can download here www.fireflow.org/download.html.

I believe what you are proposing is really a “notation” standard more than a “language”, but it might also be called a “language”. XPDL on the other hand is simply an interchange format. Because FPDL and XPDL are essentially different things, I believe you can accomplish what you want to do, but we need to clarify the roles of these proposals.

For instance “BPMN” is a notation which has been broadly adopted in the market, and it describes both the way that things look, as well as some rules about what can be connected to what. Some products use BPMN as the notation, and XPDL as the file format for interchange of diagrams. At the same time, there are many products which have invented their own notation, and use XPDL as the file format. XPDL does not include a specific notation, and does not force a product to use a particular notation.

A process product will have particular rules about how a user must draw the diagram, and what must be connected to what. XPDL does not enforce these rules. This is considered a weakness by some, because there is no guarantee that all XPDL files represent diagrams with the same rules, and subsequently there is no guarantee that all products can read all XPDL files. The reality is that XPDL was designed to work across products that had different rules, and had we incorporated a specific set of rules into XPDL, then only a very small subset of all products would be able to implement it, and subsequently it would be useless as an interchange format. For this reason, XPDL purposefully allows a product to have rules on how you can draw a diagram, but does not force them.

What we have been doing with XPDL for the last couple of year is to make sure that the BPMN notation can be completely and unambiguously implemented by all products in the same way, so that one product that implements BPMN and follows all the rules of BPMN, can exchange diagrams completely with another product that implements BPMN notation and rules.

I think then that FPDL should be positioned as a notation in the same way that BPMN is a notation. It should be possible to map FPDL notation to XPDL for exchange with other BPM products.