First, a dependency is a semantic relationship between two model elements in which a change to one element (the independent one) may affect the semantics of the other element (the dependent one). Graphically, a dependency is rendered as a dashed line, possibly directed, and occasionally including a label.

第一个依赖关系，它表示两个模型元素在语义的相关性，体现为改变其中一个元素(语义上独立的那个)会影响到别一个元素的语义(具有依赖性的那个)．图形表现上，用一条虚线表示依赖，有时还会带有方向箭头，偶而会用标签来标识依赖的具体关系．

Second, anassociation is a structural relationship among classes that describes a set of links, a link being a connection among objects that are instances of the classes. Aggregation is a special kind of association, representing a structural relationship between a whole and its parts. Graphically, an association is rendered as a solid line, possibly directed, occasionally including a label, and often containing other adornments, such as multiplicity and end names.

第二个联合关系，它表示的是类之间结构的关系，描述的是一组用来连接类的实例－－对象之间的联系．聚集是联合关系的一种特殊形式，它表示的是整体和部分之间的结构关系．图形表现上，用一条实线表示联合，有时也会带有方向箭头，或是用标签标识．通常还有其它特性，比如多重性，终端名称等．

Third, ageneralization is a specialization/generalization relationship in which the specialized element ( the child ) builds on the specification of the generalized element ( the parent ). The child shares the structure and the behavior of the parent. Graphically, a generalization relationship is rendered as a solid line with a hollow arrowhead pointing to the parent.

第三个通用关系．专用元素(子元素)在通用元素(父元素)的规格基础上构建而成，它们之间的关系被称为特定或通用关系．子元素共享父元素的结构和行为．图形表现上，通用关系被表示为一条实心线，并带有空心箭头指向通用元素．

Fourth, arealization is a semantic relationship between classifiers, wherein one classifier specifies a contract that another classifier guarantees to carry out. You’ll encounter realization relationships in two places: between interfaces and the classes or components that realize them, and between use cases and the collaborations that realize them. Graphically, a realization relationship is rendered as a cross between a generalization and a dependency relationship.

第四个实现关系，它是分类器之间的语义相关性．其中一个分类器定义说明，另一个分类器确保实现这个定义．有两个地方会用到实现关系：接口定义说明，类或组件实现这些接口定义；用例定义说明，交互实现用例所做的定义．图形表现上，实现关系被表现为一条带有空心箭头的虚线．

These four elements are the basic relational things you may include in a UML model. There are also variations on these four, such as refinement, trace, include, and extend.

这四种元素是建模时会用到的基本关系元件．来自这四种元素的变体关系有：精炼，追溯，包含和扩展．