Summary of several relationships of UML class diagram

stay UML In class diagram , There are several common relationships : generalization （Generalization）,   Realization （Realization）, relation （Association）, polymerization （Aggregation）, Combine (Composition), rely on (Dependency)

 

1. generalization (Generalization)

【 Generalization relation 】： It's an inheritance relationship , It specifies how the subclass can specialize all the features and behaviors of the parent class, such as ： Tiger is a kind of animal .

【 The arrow points to 】： A solid line with a triangular arrow , The arrow points to the parent class

2. Realization （Realization)

【 Realization relationship 】： It's a kind of interface relationship , A presentation class is an implementation of all the features and behaviors of an interface

【 The arrow points to 】： Dotted line with triangular arrows , The arrow points to the interface

3. relation （Association）

【 Connections 】： It's a relationship of ownership , It lets one class know the properties and methods of another class ; Such as ： Teachers and students , Husband and wife

Association can be two-way , It could be one-way . A two-way association can have two arrows or no arrows , A one-way association has an arrow .

【 The code is 】： Member variables

【 Arrows and points 】： A solid line with an ordinary arrow , Point to the possessed

 

Above picture , Teachers and students are connected in two ways , The teacher has many students , Students may also have more than one teacher . But the relationship between students and a course is unidirectional , A student may take more than one course , Course is an abstract thing. He doesn't have students .

 

The picture above shows the self relevance ：

 

4. polymerization （Aggregation）

【 Aggregate relationship 】： It's the relationship between the whole and the part . For example, the relationship between the car and the tire is the relationship between the whole and the part .

Aggregation is a kind of association , It's a strong correlation ; Association and aggregation are grammatically indistinguishable , We must examine the concrete logical relations .

【 The code is 】： Member variables

【 Arrows and points 】： A solid line with a hollow diamond , Rhombus pointing to the whole

 

 

5. Combine (Composition)

【 synthetic relation 】： It's the relationship between the whole and the part ., There is no department without a company        A combination relationship is a kind of association relationship , It's a stronger relationship than an aggregate relationship , It requires that the object representing the whole in the common aggregation relationship is responsible for the life cycle of the object representing the part

【 The code is 】： Member variables

【 Arrows and points 】： A solid line with a solid diamond , Rhombus pointing to the whole

 

 

6. rely on (Dependency)

【 Dependency relationship 】： It's a relationship of use , So try not to use two-way interdependence .

【 Code representation 】： local variable 、 Method parameters or calls to static methods

【 Arrows and points 】： Dotted line with arrow , Point to the user

 

 

 

The order of strength and weakness of various relationships ：

generalization = Realization > Combine > polymerization > relation > rely on

This picture below UML chart , It vividly shows all kinds of class diagram relationships ：