WebSphere Message Service Client for C/C++, Version 2.0.2 Operating Systems: AIX, Linux, Solaris, Windows

Styles of messaging

XMS supports the point-to-point and publish/subscribe styles of messaging.

Styles of messaging are also called messaging domains.

Point-to-point messaging
A common form of point-to-point messaging uses queuing. In the simplest case, an application sends a message to another application by identifying, implicitly or explicitly, a destination queue. The underlying messaging and queuing system receives the message from the sending application and routes the message to its destination queue. The receiving application can then retrieve the message from the queue.

If the underlying messaging and queuing system contains a WebSphere® Message Broker, the broker might replicate a message and route copies of the message to different queues so that more than one application can receive the message. The broker might also transform a message and add data to it.

A key characteristic of point-to-point messaging is that an application identifies a destination queue when it sends a message. The configuration of the underlying messaging and queuing system then determines precisely which queue the message is put on so that it can be retrieved by the receiving application.

Publish/subscribe messaging
WebSphere MQ V7.1 contains embedded publish/subscribe function. This function replaces WebSphere MQ Publish/Subscribe, which was supplied with WebSphere MQ V7.0. Message Service Client for C/C++ applications can use the embedded publish/subscribe function, and can use it instead of using WebSphere Event Broker or WebSphere Message Broker for publish/subscribe messaging with WebSphere MQ as the transport. Configuring Message Service Client for C/C++ to use the new function is simpler than configuring Message Service Client for C/C++ to use WebSphere MQ Publish/Subscribe, WebSphere Event Broker, or WebSphere Message Broker. Administrators and application developers need not manage publication queues, subscriber queues, subscription stores, and subscriber cleanup.
In publish/subscribe messaging, there are two types of application: publisher and subscriber.

A publisher supplies information in the form of messages. When a publisher publishes a message, it specifies a topic, which identifies the subject of the information inside the message.

A subscriber is a consumer of the information that is published. A subscriber specifies the topics it is interested in by sending subscription requests to a publish/subscribe broker. The broker receives published messages from publishers and subscription requests from subscribers, and it routes published messages to subscribers. A subscriber receives messages on only those topics, to which it has subscribed.

A key characteristic of publish/subscribe messaging is that a publisher identifies a topic when it publishes a message, and a subscriber receives the message only if it has subscribed to the topic. If a message is published on a topic for which there are no subscribers, no application receives the message.

An application can be both a publisher and a subscriber.

The embedded publish/subscribe function also provides some additional features such as retained publications and a choice of two wildcard schemes for specifying a range of topics to which an application wants to subscribe.

An application can still use a real-time connection to a broker of WebSphere Event Broker or WebSphere Message Broker for publish/subscribemessaging. This support is unchanged. Applications using WebSphere MQ Publish/Subscribe can use the embedded publish/subscribe function without change when the queue manager to which they are connected is upgraded. Properties that are set by an application, but are not required by the embedded publish/subscribe function, are ignored.


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Last updated: 24 May 2011

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