What is Multitiered Application?
出自sun对宠物商店例子的综述文档?
Partitioning a design into tiers allows designers to choose
the appropriate technology for a given situation. The Java
Pet Store demo, illustrates how its design is divided into
multiple tiers.
使用分层的方式来进行设计，可以使设计者针对具体的情况使用合适
的技术。这个Java 宠物商店的例子展示了如何把一个设计分成多层结构。
The Client tier is often the only part of the application the
user sees. The Java Pet Store demo Client tier consists of a
browser displaying web pages generated from JSP pages in the
Web tier. An administrator interface uses a spreadsheet client,
such as StarOffice software, to communicate with the Web Tier
XML messages. The Client tier communicates with other tiers
through defined interfaces.
客户层通常是用户唯一可以看到的应用程序的部分。这个宠物商店例子
的客户层是一个浏览器，它负责显示Web层中JSP页产生的web页面。一个
管理员接口可以使用一个spreadsheet客户端（例如StarOffice软件）来
和Web层交换XML消息。客户层通过定义好的接口和其他层交互。
The Web tier performs web-related processing, such as serving
HTML, instantiating web page templates, and formatting JSP pages
for display. Some objects within the Web tier act as proxies to
components in the Enterprise JavaBeans components tier.
Web层负责Web相关的处理，比如提供HTML服务，产生web页面的模板的实作，
格式化JSP页面来显示。Web层中有一些物件可以作为EJB组件层中组件的
代理。
The Enterprise JavaBeans components tier is responsible for any
processing involving Enterprise JavaBeans components. Enterprise
JavaBeans components contain the business logic of the Java Pet
Store demo, such as processing orders. EJB components also
represent the model objects of the Java Pet Store demo, including
Account and placed Orders.
EJB组件层负责任何与EJB组件相关的处理。EJB组件中包含这个Java宠物商店
的商业逻辑，比如处理订单。EJB组件也含有这个Java宠物商店的物件模型，
包括账目和处理过的订单。
Stand-alone clients and web applications in the Web tier can use
Enterprise JavaBeans components hosted by the Enterprise JavaBeans
components tier. The Java Pet Store demo demonstrates the proper
use of Enterprise JavaBeans components.
单机版客户端和网络层中的web应用都可以使用EJB组件层中的EJB组件。这个
Java宠物商店的例子展示了如何恰当地使用EJB组件。
The Enterprise Information System (EIS) tier provides a layer of
software that maps existing data and application resources into
the design of a J2EE application in an implementation-neutral way.
The EIS tier can also access applications of other organizations
or businesses, providing seamless business-to-business integration.
企业信息系统（EIS）层提供了一层软件，以一种与实现无关的方式把已存在
的数据和应用资源一起映射到一个J2EE应用程序的设计之中。EIS层通过B2B的
无缝集成使得其它的组织或商业机构也可以对其进行使用。