用例模型是以专门术语描述实际系统功能需求的原型。在用例模型中，一个实际系统功能需求被表示为一个到多个系统行为（System Behavior）。为便于描述系统行为的动态过程，在用例模型中还使用活动图（Activity Diagram）来描述系统内部状态的变化过程（还配套状态图和事件流图）。激发一个系统行为的第一信息来源和目标被称为角色（Actor），而当系统行为发生后会对第一信息来源产生反应。角色只能在系统边界以外，用例模型实际上表现了系统内外的作用与反作用的信息交流过程。UML中的用例模型分别用表示实际系统功能和与其相关的环境的图形符号体系所构成。-model based on cases with specialized terminology describing the actual needs of the system function prototype. The Use Case Model, a practical system functional requirements are expressed as a multiple system acts (System Behavior). To facilitate the descr iption of the system dynamic process, in cases with the use of model also plans activities (Activity Diagram) to describe the state of the system of internal change process (also supporting state plans and events flow diagram). Stimulate a system of the first sources of information and targets are known as role (Actor), and when the system will occur after the first source of information to respond. Only role beyond the borders of the system, with cases actually model performance of the system and outside the action and counteraction of