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8/25/2010
03:29 PM
Bruce Silver
Bruce Silver
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BPMN Model Interchange: Clearing the Hurdles

We usually think of BPMN as a diagramming standard, but it is also -- in principle -- a model interchange standard, an XML format than can be exported from tool A and imported into tool B. In reality, however, BPMN model interchange faces serious -- some would say insurmountable -- hurdles...

On my summer vacation I've been thinking a lot about the XML side of BPMN. While we usually think of BPMN as a diagramming standard, it is also -- in principle -- a model interchange standard, an XML format than can be exported from tool A and imported into tool B. BPMN 2.0, XPDL 2.1 (for BPMN 1.2), and XPDL 2.2 (for BPMN 2.0) all purport to deliver this. In reality, however, BPMN model interchange faces serious -- some would say insurmountable -- hurdles. I have been working on a number of tools to overcome these obstacles.

To achieve BPMN model interchange, you need the following:

1. An explicitly enumerated set of interchangeable model elements and attributes. The full BPMN 2.0 schema is too open-ended for unrestricted interchange. Fortunately, we now have such an enumerated list in the Descriptive and Analytic process modeling conformance classes in the BPMN 2.0 spec.
2. Modeling tools that unambiguously support all the elements and attributes in those conformance classes, meaning the mapping of diagram shapes and labels to the standard is unambiguous. We have a number of such tools today. My work has focused on two of them: Process Modeler for Visio by itp commerce, which supports both BPMN 1.2 and 2.0, and native Visio 2010 Premium, which is just BPMN 1.2.
3. XML export (as BPMN 2.0 or XPDL) from those tools. Process Modeler exports either BPMN 2.0 or (in the Pro edition) XPDL 2.1 for BPMN 1.2. There are a couple problems with it in the current build, but I expect those to be fixed shortly. Visio 2010 Premium has no native XPDL or BPMN export. (Global 360′s analystView add-in provides XPDL 2.o but does not fully support either the Descriptive or Analytic conformance classes.) The good news is I have developed a tool that produces either XPDL 2.2 or BPMN 2.0 from Visio 2010 Premium, absent a few BPMN 2.0 shapes missing from the palette: non-interrupting events, escalation, CallActivity, etc.
4. Validation of user-created models to support effective interchange. Four distinct types of validation are required:1. Adherence to the rules of the BPMN spec. Both itp and Visio 2010 offer this built into the tool. 2. Adherence to the palettes specified by the Descriptive and Analytic conformance classes. The purpose is to identify diagram elements that may not be interchangeable. WfMC provides an online tool to validate against the XPDL 2.1 conformance classes, which are similar to those defined by BPMN 2.0. I will probably create something similar for BPMN 2.0.
3. Schema validation of the exported XML, either XPDL or BPMN 2.0. You might think that tools would always produce schema-valid XML, but they don't, for two reasons: First, they either ignore the published xsd or reference an outdated version. Second, the user-created diagram may be inherently invalid. For example, if one end of a message flow is drawn dangling in space (or is improperly connected to a flow object), its required sourceRef or targetRef attribute in the XML will be missing.
4. Adherence to certain conventions that allow unambiguous serialization of the diagram. These conventions go beyond the requirements in the BPMN spec, and they could be thought of as "style rules." Many of them are also important for human readability of the diagrams and are identical to rules I require in my BPMN Method and Style certification exercises. I have created a validation tool that looks at exported BPMN 2.0 and lists violations of both BPMN rules (4.1 above) and these conventions/style rules. I originally built the tool to automate examination of student certification exercises, but it turns out to have broader value. A fundamental Method and Style principle is that the process logic should be evident from the diagram itself -- the shapes and labels, nothing more, no reference to BPMN details with no visual representation. That is consistent with the information contained in the BPMN 2.0 conformance classes, which explains the alignment of Method and Style conventions with diagram conventions needed for proper serialization.
5. Process modeling and executable process design tools that can import and edit BPMN 2.0 or XPDL that passes all of the aforementioned validation tests. This is the biggest gap right now. The primary need is to export from a business-friendly BPMN tool like itp or Visio 2010 and import into a BPMN 2.0-based BPMS like Oracle BPM11g. Today you can't do it, but it's a requirement of several of my clients (and, I hear, of numerous RFPs on the street). I'm hoping to work more with Oracle and like-minded BPMS vendors on ways to do this.
With the tools I will be providing, we should be able to get through step 4.4, and I'm hoping to begin closer dialog with Oracle (and others) on step 5. I'm vacationing on Block Island until Labor Day, but working on the tools off and on. I plan to have some of them available, at least for my clients and students, in the next few weeks.We usually think of BPMN as a diagramming standard, but it is also -- in principle -- a model interchange standard, an XML format than can be exported from tool A and imported into tool B. In reality, however, BPMN model interchange faces serious -- some would say insurmountable -- hurdles...

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