This illustration depicts the publish-subscribe model. On the left is a column in which there are three boxes: trigger mechanism, system events, and clients. The caption under them is "Supplier". In the middle are nonpersistent queues and persistent transactional queues. The caption under them is "Channel". On the right are e-mail client, OCI client, HTTP Server, and database PL/SQL procedure. The caption underneath them is "Consumer". Between the columns are arrows marked "push", pointing to the right.