Software Engineering Case Model Summary

Document directory

• How to determine the use case?
• 3. How to ensure correct use cases
• 4. use case diagram

I. Use Case Model 1. Use Case Concept

Use Cases: the functional requirements discovered when using the system should not be too complex. Simply put, you want the system to have some functions and increase the value of the system.

The Use Case model includes the use case description and use case diagram. We mainly focus on the use case description.

The Use Case model includes participants and scenarios, including success and failure scenarios.

Therefore, the use case model has multiple scenarios. Each scenario is a use case.

Use Cases must focus on providing users with an observed return value, that is, what the system can bring to users after triggering a use case.

General Use Cases are black box use cases, that is, how to implement them is not considered.

2. use case description
Each use case has a description. How to determine the use case?

(1) determine a function;
(2) write an example;

(1) major participants: persons who call system services to achieve their goals.

(2) secondary participants: persons who provide services to the system.

(3) write out the ideal requirements of relevant personnel of each project and analyze the functions.

(4) precondition: it must be true before this case is executed. For example, it must have been successfully logged on or verified.

(5) postcondition: After the use case is successfully executed, for example, the post condition of the use case is Successful Logon (Other failures are not considered ).

(6) main flow: lists the best steps.

The general steps of main flow are as follows:

(1) The participant takes action.

(2) system verification.

(3) return results.

(7) Extension flow: Expansion step, usually in the format of: (1) the system detects ** problems;

In the first step of main flow, 1a, 1b, 1C is used;

3. How to ensure correct use cases

EBP principle: Generally, use cases must follow this rule, that is, determine the main use cases.

The main use cases in the use case are repeated but meaningful. For example, it is meaningful for the cashier to collect the money multiple times because the money is collected much, but like logging on to the system, this 100-Time meaningless use case cannot be called a major use case;

(1) Use Case writing Based on EBP (Basic Business Process) principles;

(2) If you want to write and edit a, delete a and add a, you can merge it into "manage ";

4. use case diagram

Each use case description is a use case. On the left side is the primary participant (who wants the system to provide services to him) and the secondary participant (who provides services to the system );

 

The secondary participants cannot have databases, because the user does not know that the system has databases;

 

Link:

(1) Generalization relationships can be generalized in both participants and use cases.

(2) Inclusion relationship:

 

Indicates that a contains B. For example, a is managing data, and B can be adding or deleting data;

(3) extended relationships:

It indicates that D is extended by C, and D contains new functions. For example, D is used to query data, and C can be used to print data. That is, you can query but not print data. Printing data is just an extended function.

Use case description Template

The Use Case Model describes the input and output of the system based on the determination of the system boundary, determines the participants outside the system, and describes the main functions of the system through the use case, describes the interaction between external participants and the system, and uses the system as a black box to describe the functions required by the system from the user's perspective;
Use Case: Use Case name actor: Participant precondition: precondition, that is, the condition postcondition: the condition that must be met for executing the use case. If the execution is successful, the status will change to main flow: 1. the user starts a session. user input 3. system verification and feedback 4. the user repeats step 3 and Step 3 extensions: 3A: The data is invalid. error prompted