Introduction › WebSphere MQ Concepts and Terminology

WebSphere MQ Concepts and Terminology

Before exploring how to define a CA Gen distributed processing application to use WebSphere MQ, it is important to understand the concepts and terminology of Websphere MQ. This section presents the WebSphere MQ topics that have a direct influence on the definition and execution of a CA Gen WebSphere MQ DP application.

Note: If you have an understanding of WebSphere MQ, you can skip this section.

WebSphere MQ is an integrated component in the family of communication server products from IBM, and is the Message Oriented Middleware (MOM) of IBM. It simplifies the task of connecting applications across unlike operating environments. WebSphere MQ applications communicate in a loosely coupled manner. That is, rather than being components bound together through some transport protocol, each application component communicates to a WebSphere MQ component known as a queue manager.

A collection of queue managers can be deployed to support the distribution of application components across a network, where each WebSphere MQ queue manager is responsible for forwarding messages to the queue manager associated with the target of a message request. The receiving queue manager can be on the same physical machine, or on a different machine that is connected through a network. The machines and operating environments do not have to be the same type as the queue manager accepting the request, they can be any type that is supported by WebSphere MQ.

The queue manager that accepts a request from an application component is known as the local queue manager (also called the source queue manager). The queue manager associated with the target of a message request is known as the remote queue manager (or target queue manager).

Note: If an application component making a request and the application component that is the target of the request are associated with the same queue manager, then the same queue manager that acts as both local and remote queue manager.

The components of a WebSphere MQ application use a common application programming interface (API) known as the Message Queue Interface, or MQI, to communicate with their associated queue managers. Therefore, before an application component can issue any MQI calls, it must be connected to a queue manager. After the application is connected to a queue manager, the queue manager processes all MQI calls issued by the application. For the application, the queue manager is synonymous with the network, and takes care of all routing and delivery issues.

Each application component defines the data to be exchanged, where the data is handled as a string of bytes that has meaning to the communicating components. The application data, together with a collection of WebSphere MQ control information (a message descriptor) comprise a WebSphere MQ message, which is subsequently placed into one of the various WebSphere MQ queues.

WebSphere MQ queues exist independently of the applications that use them. A queue is a data structure that stores messages, and each queue has queue attributes that determine what happens when an application references the queue through an MQI call. Each queue belongs to, and is maintained by, a given queue manager, and is a local queue to that queue manager. By contrast, a remote queue is a queue that belongs to another queue manager. A given queue manager puts the messages it receives onto the appropriate queue, as directed by the application, through the MQI.