Message brokers provide business processes a channel-based publish and subscribe communication mechanism, which enables processes to communicate in a loosely coupled, anonymous mode.
A purchase order routing process can, for instance, subscribe to a message broker channel called NewOrderEntered; every time a new order message is published to the NewOrderEntered channel, the purchase order routing process is activated.
You can specify the channels to which a process publishes and subscribes. Publishers can broadcast messages on the channels and consumers such as processes and other back end resources can subscribe to them. In this way, the message broker facilitates a loosely coupled interface. You can add new publishers and new subscribers at run time.
Message brokers support event generators that can publish events from external sources to the message broker channels.
Table 4-1 lists the message broker features of WLI:
Table 4-1 Message Broker Features
Feature
Benefits
Publish and Subscribe
The publish and subscribe communication mechanism provides high-performance throughput.
Processes can subscribe dynamically to message broker channels through controls.
Static subscriptions can be specified at the start node of the process. In this case, the process starts when it receives a message from a channel to which it is subscribed.
Subscriptions can start a new process or be used within a running process to block a message.
XQuery filters can be used to refine message selection on subscription.
Message Broker Channels
WLI supports static and dynamic binding to channels.
Channel typing explicitly defines the structure of the message that the channel can route.
The channel-naming hierarchy is defined.
Event generators publish messages to channels from external sources.
Event generators can be bound dynamically to channels at run time using the WLI Administration Console.
WebLogic adapters can publish events to channels.
Message Routing
WLI supports routing from event generators to stateless processes.
Message routing takes place as a single transaction; there is no need to save the state.
Rules
Business process logic defines the trigger, transformation, and routing rules.
The business logic can be defined in the form of rules with short execution times rather than as time-consuming processes.
