Applications, one at the top and three at the bottom of the illustration, are linked to an unlabeled queue in the middle. The queue contains three messages labeled priority 3, priority 1, and priority 2 respectively. At the top of the illustration, Application A, Producer is linked to the queue with a downward-pointing arrow labeled Enqueue.

All three applications at the bottom carry the label Consumer (Rule-Based Subscriber). At bottom left, Application B carries the additional label "priority = 1" and is linked to the queue with a downward-pointing arrow labeled Dequeue. Application D carries the additional label "priority = 3" and is also linked to the queue with a downward-pointing arrow. Application C carries the additional label "priority > 1" and is linked to the queue with two arrows. One points downward and is labeled Dequeue. The other arrow points back to the queue and is labeled Register.