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UML diagram - use case diagram

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What is it? use case chart?

use case The figure was created by participant(Actor)、 use case(Use Case) and the use of the relations The static view of the system used to describe the composition of the UML diagram( This definition is taken from the Baidu encyclopedia)。 use case The diagram is able to show the various types of performers outside the system with the system in use case of relations。

What are the components of a use case diagram?

As we know from the definition, the use case diagram consists of participant(Actor)、 use case (Use Case) and between these two relations The three components, strictly speaking, use cases also include System boundary However, the use cases and participants are inside and outside the system, so the system boundary is implicitly between them, and thus the system boundary can generally be omitted when drawing the diagram.

participant: participant i.e. outside the system, But individuals who interact with functional units within the system, For example, librarians、 The borrowers are all from the library management system use case Figure. participant。 One thing to note is that, It's not just“ human” only then participant, It could also be equipment、 Other systems, etc., Any external object that interacts with the system is part of the participant, consequently, If you go deeper into the division, It's also possible to place participant Divided into initiators( take the initiative) and supporters( passively), The initiator is use case The main clients of the, Supporters are the objects that support the system。

Participants are usually represented by a small human figure, as in the figure.

use case : A use case is a system functional unit visible within the system (the functionality of the system is provided by a system unit and expressed through a series of information exchanged between the system unit and one or more participants) and can be simply understood as a function in the system, e.g. "query function", "borrow function", "return function", etc. is a use case in a library management system, and the use case is usually expressed as an ellipse, as in the figure.

relations : Information needs to be exchanged between participants and use cases, so the relationship between them is a communication relationship, usually represented by an arrow with the direction of the arrow being the initiator pointing to the use case and the use case pointing to the supporter. As pictured.

The role of use case diagrams

1. The primary role of use case diagrams is to describe the user's needs, i.e., what functions the system implements (without explaining how to implement them), so use case diagrams are mainly used in the requirements analysis phase.

2、 use case The diagram depicts who is the system participant, The system needs to provide for participant What services are provided, participant What services need to be provided to the system, Facilitate user understanding of the system, It also facilitates the developers' implementation of the system。

use case What are the characteristics of the figure?

1. Use case diagrams can be applied to the whole system or to a part of it.

2、 use case The figure is known as“ participant” A model diagram of the system functions that can be observed by external users of the。(《UML Reference Manual》)

Describe what services the system can provide or what behavior it has from outside the system

3. The use case diagram lists the participants and use cases in the system, and describes which participant is involved in the execution of which use case (or is referred to as initiating which use case).

4. Use case diagrams are mostly used for static modeling (mainly requirements modeling).

use case Figure Application Examples

The following is a small example of a student examination system.

In this simple use case diagram, "Login" and "Exam" are the use cases in the exam system, "Student" and "Student Information System" are the participants (where students can login and take exams, and students' student numbers and passwords are stored in the student information system, so the exam system needs the support of the student information system, so "Student" is the initiator and "Student Information System" is the supporter).

The following is also a brief use case diagram of the server room charging system.

This is my first time dabbling in the subject, so I would appreciate any guidance on any shortcomings or gaps.

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