1. VO: It is actually vague, usually refers to ValueObject and ViewObject 2. ViewObject, the interface exhibits the required object, such as FORMBEAN 3 for Struts. Value Object, early as the general name of ValueObject and Transfer Object. In fact, the true meaning of Value Object is its content, not identity 4. Transfer Object: Data transfer objects, subjects between applications, in a distributed application, usually improves overall performance 5. PO: Perhaps, Persistent Object, basically Entity, in different architecture and implementation, these objects may be repeated, or may not overlap. If you want to make a framework for all systems, you need to strictly distinguish between each object. For example, JDO's PO cannot be used as TO, it should not be separated from PM, for example, you can choose to use ViewObject (such as struts's formbean) as TO, but it is not suitable in Tapestry and Webwork. But in many times, it is most important to be convenient, don't overdee design.
Application: http://www.hibernate.org.cn/61.html
