Indeed Frank.
The reason being you dropped the named association "participates in" between Actor and Joint Action. And that meant a lot! Perhaps a better solution would be to have a separate Willingness class with a named associations between Actor, Joint Action and Willingness. Even better if we model that Joint Action has a dependency on Willingness. (Is this true? I think so).
Incidentally, what is that association class "Participates" between Joint Action and Action intended to model? Participates is not a noun so this seems a bit odd in a class diagram. Plus, I don't know what it means. Don't know why I did not catch this before.
- J
