Several relationships of UML

Extended relationship :

If you can from the execution of a use case , Switch to another use case when needed , After execution, continue to execute the case before returning

Exists between use cases 《extend》 Relationship .

Inheritance relationships ：

Have properties and behaviors common to other transaction types , Each specific thing type inherits it , And implement specific operations that are appropriate for you .

1、 What is a class diagram

Class diagram (Class diagram) It is mainly used to describe the structural design of the system . Class diagrams are also the most commonly used UML chart , The class diagram can show the class 、 And the relationship between them .

2、 The elements of the class diagram

The class diagram contains the following model elements , Namely ： class （Class）、 Interface （Interface）、 rely on （Dependency） Relationship 、 generalization （Generalization） Relationship 、 relation （Association） Relationship 、 Aggregate relationship （Aggregation）、 synthetic relation （Composition） And the implementation （Realization） Relationship .

2.1 class （Class)

In object-oriented （OO) Programming , A class is an abstraction of a group of objects with the same characteristics in the real world .

2.2 Interface （Interface）

An interface is a special class , Has the structure of a class but cannot be instantiated , Can only be realized . stay UML in , The interface uses a small circle with a name to represent .

2.3 rely on （Dependency） Relationship

A dependency is a dependency between two or more classes , For example, plants depend on soil . Dependencies can also be subdivided into 5 Types , They are bindings （Binding） rely on 、 Realization （Realization） rely on 、 Use （Usage） rely on 、 abstract （Abstraction） Reliance and authorization （Permission） rely on .

Dependencies are represented by dashed arrows , The arrow points in the dependent direction .

2.4 generalization （Generalization） Relationship

Simply put, it is the inheritance relationship between classes . stay UML in , The generalization relation is a hollow triangle + A solid line , The arrow points to the parent class .

2.5 polymerization （Association） Relationship

Aggregation is a weak coupling relationship between classes , For example, an array of strings and a string are aggregation relations . stay UML Middle class diagram , Use a hollow diamond for aggregation + Solid line arrow , The arrow points to the class being aggregated .

2.6 Combine （Aggregation） Relationship

A composite relationship is a relationship between a whole and a part of a class , If a frog has four legs , The relationship between frogs and frog legs is a combinatorial relationship . stay UML In class diagram , The combination relation is a solid diamond + Solid line arrow , The arrow points to the class being composed .

2.7 relation （Composition） Relationship

Association is a kind of interaction between classes , The direction of influence is the direction of correlation . stay UML In class diagram , The combination relation is represented by a solid arrow .

2.8 Realization （Realization） Relationship （ Interface ）

Generally speaking, the implementation relationship is for the relationship between classes and interfaces . stay UML In class diagram , Empty triangle is used to realize the relationship + Dotted line .

3、 Simple class diagram example

How severe ：

UML The degree of association in refers to how many instances of one class can be associated with another class .

Symbol description ：

1： One

1…1： One

0…*： Zero or more

*： Zero or more

1…*： One or more

0…1： Zero or one

The task of the requirements analysis phase is ： To deal with the real world ( organization 、 department 、 Enterprises, etc ) Conduct a detailed investigation , In understanding the overview of the current system , In the process of defining new system functions , Determine system boundary 、 Collect basic data supporting system objectives and their processing methods . One of the tasks in the logic design phase is to further standardize the relational schema .

Entity class ： It represents entities in the system domain

Boundary class ： The boundary class is the user interface of the system , Interact directly with external participants of the system , Exchange information with the system

The control class ： Control class is the interaction between objects in the control system , It is responsible for coordinating the work of other classes , Implement control over other objects

Software

Components

stay UML in , Component means “ Reusable parts in the physical packaging of a set of model element instances ”

Components are the physical realization of system functions （ Such as source code file ）, It implements logical model elements defined in class diagrams or interaction diagrams

Components can include **** Code base and runtime files

There are only dependency relationships among components . Dependencies require that one class compile before another .

Components can be viewed as different stages of development （ Compile time 、 Link time and runtime ） The results of

In a project , The definition of components is often mapped to the programming language and the development tools used