Common Mechanisms
通用机制
The UML is made simpler by the presence of four common mechanisms that apply throughout the language: specifications, adornments, common divisions, and extensibility mechanisms. This chapter explains the use of two of these common mechanisms: adornments and extensibility mechanisms.
通过四个通用机制使得UML更简单，它们将应用遍及这门语言：详述，修饰，公共部分和扩展机制．这章讲解其中两个通用机制的用法：修饰和扩展机制．
Notes are the most important kind of adornment that stands alone. A note is a graphical symbol for rendering constraints or comments attached to an element or a collection of elements. You use notes to attach information to a model, such as requirements, observations, reviews, and explanations.
备注是最重要的一类修饰，需要单独说明．一个备注是一个表达约束或是为一个元件或是一个元件集合附加注释的图形符号．你使用备注为一个模型附加信息，如需求，资料，回顾和说明．
The UML’s extensibility mechanisms permit you to extend the language in controlled ways. These mechanisms include stereotypes, tagged values, and constraints. A stereotype extends the vocabulary of the UML, allowing you to create new kinds of building blocks that are derived from existing ones but that are specific to your problem. A tagged value extends the properties of a UML stereotype, allowing you to create new information in that element’s specification. A constraint extends the semantics of a UML building block, allowing you to add new rules or modify existing ones. You use these mechanisms to tailor the UML to the specific needs of your domain and your development culture.
UML的扩展机制允许你在可控的方式内扩展这门语言．这些机制包括模式化，标签值和约束．一个模式化是扩展UML的词汇表，，允许你从已存在的词汇中提取，专门针对你的问题创建一个新的构建块，一个标签值扩展UML模式化的特性，允许你在那个元素的规则之内创建一个新的信息．一个约束扩展UML构建块的语义，允许你增加新的规则或是修改现有的规则．你使用这些机制来剪裁UML以适应你的领域和你的开发习惯的需要．
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