Remote procedure call (RPC) systems, including Java RMI, are synchronous -- the caller must block and wait until the called method completes execution, and thus offer no potential for developing loosely coupled enterprise applications without the use of multiple threads. In other words, RPC systems require the client and the server to be available at the same time. However, such tight coupling may not be possible or desired in some applications. Message-Oriented Middleware (MOM) systems provide solutions to such problems. They are based on the asynchronous interaction model, and provide the abstraction of a message queue that can be accessed across a network. Note, however, that messaging here refers to asynchronous requests or events that are consumed by enterprise applications and not humans as in electronic mail (email). These messages contain formatted data that describe specific business actions.
大意为：
RPC是同步的通信，在一个消息发出后，消息的发送者必须等待这个事件被处理后然后才能进行接下来的工作，在等待期间，该发送者处于阻塞的状态。在RPC系统中，要求client和server必须同时在线，但这一要求通常很难满足。与此同时，MOM则是基于异步交互机制的，并且抽象了一个消息队列。这一消息队列允许通过网络来进行访问。需特别注意的是，此处所言的“消息”指的是企业应用中产生的请求或事件，而不是大家常用的email消息。MOM中传递的消息包含已经被规格化了得数据。这些数据是用来表述特定商业事件（动作）的。
A JMS application is composed of the following parts:
- A JMS provider: A messaging system that implements the JMS specification.
- JMS clients: Java applications that send and receive messages.
- Messages: Objects that are used to communicate information between JMS clients.
- Administered objects: Preconfigured JMS objects that are created by an administrator for the use of JMS clients.
- JMS提供者：一个实现了JMS标准的消息系统。
- JMS用户：发送和接收消息的java应用。
- 消息：在JMS的各个客户间进行传递的对象。
- 管理对象：由管理者创建的，被JMS客户使用的预设置的JMS对象。
Getting Started with Java Message Service (JMS)
location: http://java.sun.com/developer/technicalArticles/Ecommerce/jms/
The Java Message Service API
location: http://docs.oracle.com/javaee/1.4/tutorial/doc/JMS.html
入门教程