15.1 Overview of the Java Message Service The Java Message Service is an application programming interface that allows programs to communicate information via messages. The API allows for loose coupling between these programs by providing: Reliable messaging - JMS can be set to ensure that a message is delivered once and once only. Asynchronous - Allowing the sender and receiver to be online at different times, providing greater flexibility; especially convenient when dealing with portable devices. Synchronous delivery - Traditional send-and-wait-for-reply type messaging is supported. One-to-one messaging - Traditional point-to-point messaging is supported. One-to-many messaging - Publish-and-subscribe messaging is now supported in the WebSphere Everyplace Deployment Client. 15.1.1 Definition of terms In order to understand the concepts of JMS, we need to discuss several terms: Messaging domains