This figure shows 5 boxes with 6 lines connecting them:

1. An arrow from a Publisher (Agent) box to a Topic (Subject Channel) box

2. A "receive notification/message" arrow from the Topic to a Subscriber (Agent) box

3. A "register" arrow from the Subscriber to the Topic

4. A "subscribe" arrow from the Subscriber to the Topic

5. A line between the Topic box and a Subscriptions box

6. A line between the Topic box and a Rules box