In the past 2 months I have been in and out working with other persons to fix the problems in the ArgoUML's subsystem model-mdr (see issue #4946). This is a core part of the ArgoUML implementation and it basically wraps NetBeans MDR into an implementation of the ArgoUML model subsystem.
MDR is based in JMI (a standard from the Java Community Process), which is itself based in MOF (a standard from OMG). I was more or less familiar with the ideas behind MOF, but, as always, the devil is in the details and I'm now reading the standard so that I'm not bumping so much on problems.
My lack of knowledge about MOF was made worse by the sources of the several jars from MDR not being included in the ArgoUML repository. Also, unusual for open source projects MDR doesn't make it available as a download - you must checkout the sources with Mercurial (more on this latter) or CVS. Even so, it doesn't contain the sources for jmi.jar and mof.jar. The MOF and JMI standards don't have a zipped javadoc to help when you bump into unexpected problems in the debugger. All this is making the whole exercise harder than needed!
TODO: get my hands on the jmi.jar and mof.jar sources!