In general, I am searching for a way to Model business processes. I found UML and BPMN quite often as an answer to this. Now I want to check this models with a Program. There i
A workaround with the problem of the answer of @user2757652 is to modify BPMN20.xsd and Semantic.xsd downloaded from http://www.omg.org/spec/BPMN/2.0/. other files can be used unchanged.
I replaced flowElement ref with its ancestors (in Semantics.xsd) and rootElement ref (in BPMN20.xsd) with process and collaboration. you might relplace all ancestors of rootElement. altough the resulting xsd is not standard and could validate some invalid BPMN XMLs, it fulfilled my needs
you can download the modified version from Github Gist