WebSphere MQ defines the following types of messages:
A simple message with no expected reply.
A message with an expected reply.
The answer to a request.
A message that describes an event such as an error.
Each application component can access one or more queues to process a flow of one or more messages through its queue manager. For example, an application component can have a request message placed in a target queue managed by a remote queue manager. The same application receives the reply to the request from a local queue managed by its associated queue manager. The key thing to note here is that there does not have to be a network connection between the application components, only a connection to their respective queue managers.
As WebSphere MQ supports different types of messages. It also supports different types of queues. Each queue must have a unique name within a given queue manager. Before an application can make use of a queue, the queue must first be created and made known to its owning queue manager. Additionally, an application must open the queue so that it can be accessed for its expected usage (such as input, output, and inquiry). Each queue has many attributes that define the allowed behavior for the queue to its owning queue manager.
The queue type attribute helps establish the intended use of the queue. WebSphere MQ supports the following types of queues:
A queue owned by the queue manager to which a given application is connected. Application programs can Put messages to, or Get messages from, local queues.
Additionally, each queue manager can have several special purpose local queues that support the processing of application messages by the queue manager.
Note: Applications cannot get messages from remote queues.
A queue owned by a queue manager other than the local queue manager. A local queue manager defines a remote queue with only sufficient information to locate the queue. The queue manager that owns the queue manages all attributes for the queue. Remote queues can only be used to Put messages. It is not possible to Get messages from remote queues.
An application processes an alias queue as though it were an actual queue. The owning queue manager maps any request for the alias queue to the actual queue.
A model queue is not an actual queue. It acts as a template containing a set of queue attributes. An application uses a model queue when it needs to create a dynamic local queue.
A temporary local queue that is created on demand by an application request. The model queue, specified when the dynamic queue is created, provides the collection of queue attributes that are needed by a queue manager before it can create the dynamic queue.
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