Hi!
Have you considered classifying the different actions?
For instance, categories related to message topics may be create, reply and read.
Then if you have a message topic with the id 12345, you could retrieve the creator of the topic using, for instance,
http://mymessageboard.com/topics/12345/creator and the people that have replied to the topic using, for instance,
http://mymessageboard.com/topics/12345/replies.
To retrieve the topics read by the user with id 45678, you could use
http://mymessageboard.com/users/45678/readmessages and to retrieve unread messages
http://mymessageboard.com/users/45678/unreadmessages.
Hope this will give you some new ideas.
Best wishes!
