UML中Association(关联), Aggregation(聚合), Composition(组合)和Dependency(依赖)辨析

Association, Aggregation, Composition and Dependency 

Association vs. Dependency

Association

Association的定义：

描述两个类之间的结构关系：一个类的实例连接到另一个类的实例

An association is a structural relationship between classes that specifies that objects

of one class are connected to objects of another class。

#严格的说，An association represents a structural relationship that connects two classifiers

 通常也可以用class泛指其他3类。

Classifiers: class、interface、data type、component。

Association有5种类型：

1. Bi-directional:

2. Uni-directional associations:

3. Association class:

4. aggregation（Basic aggregation）:

5. Composition (Composition aggregation)

Reflexive associations

Association举例：

Bi-directional:

Association class:

Dependency

Dependency的定义：(From UML Spec)

A dependency signifies a supplier/client relationship between model elements where the modification of the supplier may impact the client model elements. A dependency implies the semantics of the client is not complete without the supplier. The presence of dependency relation