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What are the components involved?
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 a WebSphere MQ message, and the subject of the information is identified by a topic. The publisher specifies the topic when it publishes the information, and the subscriber specifies the topics on which it wants to receive publications. The subscriber is sent information about only those topics it subscribes to.
Interactions between publishers and subscribers are all controlled by a broker. The broker receives messages from publishers, and subscription requests from subscribers (to a range of topics). The broker's job is to route the published data to the target subscribers.
Related topics can be grouped together to form a stream. Publishers can choose to use streams, for example to restrict the range of publications and subscriptions that a broker has to support, or to provide access control. The broker has a default stream that is used for all topics that do not belong to another stream.
The broker uses standard WebSphere MQ facilities to do this, so your applications can use all the features that are available to existing WebSphere MQ applications. This means that we can use persistent messages to get once-only assured delivery, and that your messages can be part of a transactional unit-of-work to ensure that messages are delivered to the subscriber only if they are committed by the publisher.
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