# Introducing the Message Broker

The Message Broker provides typed channels, to which messages can be published, and to which services can subscribe to receive messages. You can design your system for subject-based or content-based routing of messages:

- The Message Broker provides typed channels, which you can use to design subject-based routing of messages. Messages can be published to these typed channels, and business processes can subscribe to the channels that receive those messages.
- The Message Broker includes a message filtering capability that allows you to design content-based routing. Using XQuery filters, subscribers to Message Broker channels can filter messages on the channels based on content and process rules.WebLogic Integration provides a mapping tool that allows you to create the XQuery filters.

Two Message Broker controls are available when you build WebLogic Integration applications: Message Broker (MB) Publish and Message Broker (MB) Subscription. Business processes use MB Publish controls to publish messages to channels and MB Subscription controls to dynamically subscribe to channels and receive messages:

- You bind the Message Broker channel to the MB Publish control when you declare the control, but it can be overridden dynamically.
- When you create an instance of a MB Subscription control for your business process, you bind the channel and optionally, an XQuery expression for filtering messages. However, in the case of a MB Subscription control, the bindings cannot be overridden dynamically.

In addition to the dynamic subscriptions you design at the Control nodes in your business process, you can design static subscriptions at Start nodes. A business process that is subscribed to a Message Broker channel at its Start node starts when a message is received on the channel to which it is subscribed.

To learn more about using the Message Broker controls in WebLogic Integration applications, see Message Broker Controls.