Frank Michael Kraft's Blog

This is my BPMN 2.0 Overview Map.

It shows a Choreography model in the middle, Orchestration with public Processes and private Processes, that belong to the public Processes.

Systems integration is the realization of the underlying business processes. This sounds so simple. But in reality there is often a misalignment between the business process design and the systems design. It is the wrong way to just implement business processes, that are as they are today or that are designed without discretion of the principles of loose coupling.

Often system designers need knowledge about how business processes work, but on the other hand business process designers need knowledge about how system integration works. As long as both sides are willing to learn and willing to share the knowledge, it is possible to come up with common principles of modeling, that avoid the most common mistakes, that lead to project cost overrun or failure.  I say it clearly what I mean: using BPMN 2.0 choreography modeling language in itself is no gurantee for success. But: It is a VERY useful tool for the communication between the business and system experts, which is a necessary condition of success.

So in other words, it is necessary, that the process design follows the principles of loose coupling of business processes. That is no design task, that can be solved by system designers alone, if the business process is modeled in a tightly coupled way. In other words: If the business process is designed in the right way – in the loosely coupled way – then the system design is without a hitch. If the business process is designed in the wrong way – there is no way to save the project on the system design level.

So are business experts forced to design business processes different, just to make the job of system designers easier? No. If it is designed that way, it is a better business process. It would work even better even if there was no system, but just paper and phone. It is more tolerant to errors. It gives the individual more freedom to decide. It makes it easier to reach the goal. Yes, it requires a little bit more brain power than just modeling the sunny day case. But in the end it pays off abundantly.

And in my eyes this is good news. It is NOT the system programming that dominates the design and dictates the constraints. It can be the business process needs again, that prescribe the way to go. And that is why BPMN 2.0 is so helpful, because it starts with the business process model.

At the Workflow Management Coalition BPMN Industry Day we also discussed about the implications, that BPMN 2.0 now has a meta model. In itself this is a very good thing. However some problems appear, when thinking about backward compatibility, especially with XPDL as de-facto standard for model exchange. If there are models, which are incomplete, but they still need to be exchanged, how can this be handled, if the BPMN 2.0 metamodel requires strict cardinality conformity, that was not required by XPDL? The same problem appears in tools in general, if the model is in an incomplete state and it is saved. Tools need to react gracefully to this situation, otherwise the usability of the tool is harmed.

So if in this example the incomplete model is validated against the meta model, then it fails, because the meta model requires at least two participants for the conversation node. However it makes completely sense to have the cardinality 2..* in the metamodel, because there is no meaningful Conversation without at least two participants. A possible solution would be to water down the metamodel. This is not discussed for BPMN 2.0, but may be for XPDL.

So in this watered down metamodel the participants cardinality is only *, allowing for 0 participants as well. The validadion succeeds, but the semantic suffers. Furthermore the check has to be done whatsoever at some stage. So watering down the metamodel is not a good idea in my view. Instead the solution should be a model lifecycle.

In this proposal the model itself has a lifecycle, which can be active or inactive. If the model is inactive, the validation reacts gracefully against the metamodel. Only if the model is active, the validation fails, but this is indeed intended. So it is unter the control of the modeler, if he wants the full strength of the validation or not.

Such a model lifecycle is not planned in BPMN 2.0 as far as I know, but I think it is a good idea and should be considered. There is a MOF 2.0 Facility and Object Lifecycle Specification that might be considered to be used in order not to invent something new that exists already.

On the BPMN & XPDL Industry Day of the WfMC Thought Leadership Summit one topic of discussion was the current status of BPMN Diagram Exchange.

In the BPMN 2.0 Spec there is a proposal, that builds on a generic OMG proposal, which is not finalized and which will be standardized independent of the BPMN 2.0 standardization.

In this proposal the idea is to have a Diagram Interchange Model independent from the Domain Model, which is in my opinion, a good idea. It is generic, so that other diagram types could be modeled. The diagram validation is done agains a so called Diagram Definition Model, which is also new. The Diagram Definition Model defines, which Attributes a Diagram Interchange node or connector can have, the allowed references and additional (OCL) constraints. Furthermore each Diagram Interchange node or connector is refers to a Domain Model class – in this case a BPMN Task or Gateway or Sequence Flow for example.

Advantages I see:

• Seperation of Model and View – Model maintenance
• Multiple Diagrams for the same underlying BPMN model are possible
• Generic format for different diagram types – tools can use synergies

Disadvantages I see:

• Tools vendors can not use XSD validation. They have to implement the validation against the Diagram Definition.
• The constraints of the Domain model (e.g. Sequence Flows can only be connected to …) must be repeated in the Diagram Definition Model.
• Grafical Attributes (e.g. line thickness) must be repeated as per modeling element.
• Attribute Format (name / value) too generic in my view.

The XPDL Format used to include the Graphics Info into the Elements of the Domain model.

This is simple and straight, and current tools support it, but has the disadvantage, that it is not possible to have one modeling element (e.g. one process) appear in different diagrams. Instead, the modeling elements must be repeated as per diagram, which has many disadvantages in model execution, analysis and model driven development. The Signavio modeler, which was discussed at the meeting, follows the same approach. However it is good as long as only diagrams are drawn for visualization purposes.

Because the BPMN Digram Exchange Proposal was too generic for some, Bruce Silver proposed an BpmnDI.XSD for a concrete XSD validation.

This approach repeats basically all or many BPMN domain modeling elements. This of course is the disadvantage, because it is but a redundant repetition of the already defined domain model. However it is no complete repetition, because the gateway type for example is not included. So a tool must look into the domain model anyway to render the gateway.

Within this discussion it came to my mind, how the GMF (Graphical Modeling Framework) solves this question. I think it is well worth to have a look at this approach, because I think it may be a good compromise.

The GMF defines a Grafical Definition Model, which only defines Shapes. This is simple to understand and straight. Then it defines a Mapping Model. Within the mapping models, nodes and connections are grouped as needed. For example it defines, that there is a node lane which can contain node Activity and Sequence Flow. As a followon the Acitivty node is connected to the Activity domain class and the Shape, that descibes how an activity should look like. The shape can be re-used, which is an advantage of the BPMN Diagram Exchange Approach. The Structures of the Diagram is already contained in the Mapping Model, so it can be serialized to XMI and XSD, which is also an advantage. However still the diagram logic is separated from the Domain Model, which is an advantage over XPDL. And it is a very generic model, which is an advantage over a mere BpmnDI.xsd.

I personally worked with the GMF, and found it quite practical. I am not proposing to use GMF per se, but maybe the approach should be further considered.