Hi Gustaf,
Indeed, the best way would be to pass the creator of the content item. However, I hit the problem, because of a constraint in calendar pkg: The owner must be one, and only one, personal calendar.
Thus, I have to option:
1. Create a fictitious party and party_type;
2. Remove calendar constraint;
So far, I opted for solution 1. However, I'm going to study more the scenario, then I can have better and more enlightening ideas.
p.s. Attachment is not a solution because, by definition, the content item will never have an attachment.