Three applications, one at the top and two at the bottom, each with a pair of queues labeled Inbox and Outbox, are linked through Oracle Streams AQ Message Propagation Infrastructure in the middle. Each application is labeled Producer and Consumer. Arrows labeled Enqueue point from each application to its Outbox, and arrows labeled Dequeue point to each application from its Inbox. Application A, at the top of the illustration, resides in Database 1. Application B and Application C, at the bottom of the illustration, reside in Database 2.
The Outbox of Application A is linked to the Inbox of Application B by an arrow that passes through the Message Propagation Infrastructure. Similar arrows link the Outbox of Application B to the Inbox of Application C and the Outbox of Application C to the Inbox of Application A.