Publishers and subscribers

Publishers and subscribers are applications that send and receive messages (publications) using the publish/subscribe method of messaging. Publishers and subscribers are decoupled from one another so that publishers do not know the destination of the information that they send, and subscribers do not know the source of the information that they receive.

The provider of the information is called a publisher. Publishers supply information about a subject without needing to know anything about the applications that are interested in the information.

The consumer of the information is called a subscriber. The subscriber decides what information it is interested in, and then waits to receive that information. Subscribers can receive information from many different publishers, and the information they receive can also be sent to other subscribers.

The information is sent in an IBM MQ message, and the subject of the information is identified by a topic string. The publisher specifies the topic string when it publishes the information, and the subscriber specifies the topic strings on which it wants to receive publications. The subscriber is sent information about only those topic strings to which it subscribes.

IBM WebSphere MQ Version 7.0 and later queue managers, use a Pub/Sub Engine instead of a broker to control the interactions between publishers and subscribers. The Pub/Sub Engine receives messages from publishers, and subscription requests from subscribers. The Pub/Sub Engine's job is to route the published data to the target subscribers.