Juliane Dehnert Four Steps Towards Sound Business Process Models. 66-82 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2472&spage=66 2003 conf/dfg/2003 Petri Net Technology for Communication-Based Systems db/conf/dfg/petri2003.html#Dehnert03