The diagram "http://www.wfmc.org/standards/model.htm" shows the parts where your CMS can cooperate with.
The book "http://www.wfmc.org/information/handbook2003.htm" and 85 others contain uses cases for this kind of application.
How do you think about a cooperation with the tools that can be found by the search "http://pharos.inria.fr/Java/query.jsp?text=workflow" at Java-Channel.org?
Do you find the documents "http://citeseer.org/cs?q=Workflow+Management" interesting?
Workflow processes can be described by the editor "http://JaWE.enhydra.org/". They will be executed by engines like "http://WfMOpen.sourceforge.net/" or "http://shark.enhydra.org/". The execution will generate events, activities and deadlines that I suggest to view and control by your calendar application.
How do you think about workflow modelling patterns?
Which of them will be implemented by your software?