A class diagram shows a set of classes, interfaces, and collaborations and their relationships. These diagrams are the most common diagram found in modeling object-oriented systems. Class diagrams address the static design view of a system. Class diagrams that include active classes address the static process view of a system. Component diagrams are variants of class diagrams.
类图显示的是类，接口和交互集及他们之间的关系．这些图是构建面向对象系统模型时最普通的图．类图处理系统的静态设计视图．类图中包含的活动图，处理系统的静态过程视图．组件图是类图的变化形式．
An object diagram shows a set of objects and their relationships. Object diagrams represent static snapshots of instances of the things found in class diagrams. These diagrams address the static design view or static process view of a system as do class diagrams, but from the perspective of real or prototypical cases.
对象图显示的是对象集及它们之间的关系．对象图表现实例的静态映像，那些实例来自于类图中建立的元件．对象图就象类图一样处理系统的静态设计视图或是静态过程视图，不同的是它处理真正的或典型案例的视图．
A component diagram is shows an encapsulated class and its interfaces, ports, and internal structure consisting of nested components and connectors. Component diagrams address the static design implementation view of a system. They are important for building large systems from smaller parts. (UML distinguishes a composite structure diagram, applicable to any class, from a component diagram, but we combine the discussion because the distinction between a component and a structured class is unnecessarily subtle.)
组件图显示已封装的类和它的接口，端口，及其内部由嵌套组件和连接器组成的结构．组件图处理系统的静态设计实现视图．由更小的部件构建成更大的系统时，组件图是非常重要的．(组合结构图与组件图不同，组合结构图适用于任何类，但是我们在这里一起讨论，因为组件和结构类只有细微不同，不需要区别讨论．)
A use case diagram shows a set of use cases and actors (a special kind of class) and their relationships. Use case diagrams address the static use case view of a system. These diagrams are especially important in organizing and modeling the behaviors of a system.
用例图显示一组用例和参与者(一种特殊的类)及其它们之间的关系．用例图处理系统的静态用例视图．这些图对于系统的组织和建模行为尤其重要．
原文：http://blog.csdn.net/listen_snow/article/details/31751859