The documentation has a small section on Process Virtual Machine API with a small code sample. However in the forums i'm reading that ProcessDefinitionBuilder is considered "impl" and should therefor not be relied upon.
So I currently have a need to generate processes, is the recommended way then using the processdefinitionbuilder or constructing the necessary XML by hand ?
yaoqiang (http://bpmn.sourceforge.net/api/index.html) also has a model api, but that one lacks the activiti extensions obviously. I think i'll try jaxb then, though i'm not fond of its verbosity.