| Messaging enables asynchrony and an interface style that is required for loosely coupled interfaces between applications. Our discussion of enterprise-capable messaging has shown that producers and consumers have different perspectives on the messages they exchange. The producer has a contract with the message server that ensures that the message will be delivered as far as the server. The server has a contract with the consumer that the message will be delivered to the consumer. The separation of these two operations is a key benefit of asynchronous messaging. It is the role of the messaging system to ensure that messages get to where they are supposed to go, in accordance with the QoS settings associated with the message. Through message acknowledgment, message persistence, and transactions, MOM provides a strong backbone that guarantees that your business-critical data will travel reliably throughout your global enterprise. An ESB can abstract away the low-level details of using MOM by removing the dependencies of writing messaging behavior such as channel definitions and QoS options into the application code. With an ESB, these details are encapsulated in a container-managed environment that is configured through an administrative tool interface. |