UML (use case diagram, class diagram, object diagram, package diagram)

  One 、 Use case diagram

• Use cases ： Use cases represent the functions of the system , A use case is a general description of system functions , The use cases of the system constitute all the functions of the system . Use cases can be applied to the whole system , Use cases can also be applied to a part of the system , Such as subsystem, etc . A system usually requires multiple use cases to describe system requirements . The use case is represented as an ellipse .

• participants ： The actor is the initiator of the use case , It is outside the use case and can initialize a use case , Are participants outside the system , It can be a user 、 External hardware 、 Other systems .

• relation ：（ Actors and use cases ）

• generalization ：（ Participants and participants ）

• contain （ rely on ）： When common behaviors can be extracted from two or more original use cases , Or when it is important to find that a component can be used to realize some functions of a use case , Inclusion relationships should be used to represent them .( The arrow points to the included party )

• Expand （ rely on ）： If a use case clearly mixes two or more different scenarios , That is, many things may happen according to the situation . We can divide this use case into a main use case And one or more sub use cases , The description may be clearer .( The arrow points to the expanded side )

• Comparison of inclusion and extension

• Use case model ： 

Two 、 Class diagram

• class ： Class can be divided into 3 Types ： Entity class ( The relationship between saving data and maintaining data )、 Interface class ( Be responsible for interacting with the outside world )、 The control class ( Responsible for business and coordination entities Working with interface classes ),(public,private,protected, Use them separately “+”,“-”,“#” The sign means ).

• Connections （ Ownership ）

   1. Two way connection    

    2. One way Association

    3. Association and ternary Association

   4. Combine ( The whole does not exist , Part does not exist )

   5. polymerization ( Members can exist apart from the whole )

•   Generalization relation （ Inherit ）( The arrow points to the parent class )

•   Dependency relationship （ Use relationship ）（ The arrow points to the dependent party ）

•   Realization relationship

• Class diagram model

3、 ... and 、 Object graph

• Object graph ： Object graph (object diagram) Shows a group of objects at a certain time and the relationship between them . The object graph can be
  As an example of a class diagram , Used to express the state of each object at a certain time .
• Representation ：

•   Object graph model

Four 、 Package diagram

• Package diagram ： The package diagram is in UML A combination of model elements represented in symbols similar to folders . Each element in the system can only be owned by one package , One package can be nested in another package . Using a package diagram, you can group related elements into a system . A package can contain accessory packages 、 Charts or individual elements .
• Dependencies of package graph ：

• The problem of circular dependence ：

• Package Introduction ：

• Package graph model ：