Thank you Esteban,
I will try this next. However, shouldn't ServiceTask be ok according to the BPMN 2.0 Spec?
http://community.jboss.org/servlet/JiveServlet/downloadImage/2-622065-16901/450-329/Capture2.PNG
I basically just copied the example BPMN2-ServiceProcess and modified it a bit by hand.
I am still trying to find out,which editor is the best for me... I am having troubles with Oryx as well as the BPMN 20 Eclipse editor plugin.
I recreated the Example BPMN2-ServiceProcess with the BPMN 20 Eclipse editor plugin, the output looks nice, however the engine does not run it...