A summary of the use case model of software engineering

One, use case model
1. Use Case Concepts

Use cases: The functional requirements found when using the system should not be overly complex, simply what you want the system to be capable of, to increase the value of the system.

Use case model includes use case description and use case diagram, we mainly put the center on the use case description.

Use case models contain participants and scenarios, including success scenarios and failure scenarios.

Therefore, there are multiple scenarios in the use case model, and each scenario is a use case.

Use cases must focus on providing the user with observable return values, which is what the system can bring to the user after triggering a use case.

General use cases are black box use cases, that is, do not consider how to implement them.

2.Use Case Description
Each use case has a description. How to determine the use case.

(1) Determine a function;
(2) write a use case;

(1) Main participant: The person who invokes the system service to accomplish the goal.

(2) Secondary participant: The person who provides services to the system.

(3) write down the ideal needs of each project person and analyze the function from it.

(4) Precondition: Must be true before executing to this use case, such as having to log on successfully or pass validation.

(5) Postcondition: After successful execution of this use case, such as the post-condition of a login use case is a successful login (regardless of other failures).

(6) Main flow: List the most desirable steps.

The general main flow steps are as follows:

(1) The participant takes action.

(2) System verification.

(3) Returns the result.

(7) Extension flow: Extended step, usually in the form of: (1) The system detects * * problem;

The first step in main flow is extended with 1a,1b,1c; 3. How to ensure the right use case

EBP principle: The general use case needs to abide by this rule, that is to determine the main use case.

The main use case in the use case is some repetitive but meaningful things, such as the cashier to collect money, repeated several times is meaningful, because the money is more, but like the login system, this does not make sense for 100 of use cases, can not be called the main use cases;

(1) Use case writing of the EBP (basic business process) principle;

(2) If you want to write edit a, delete a, add a, you can merge into "management a"; 4. Use case diagram

Each use case description is a use case and the left side is the main participant (who wants the system to serve him) and the secondary participant (the person who provided the system service);

You cannot have a database in a secondary participant because you do not know that the system has a database at the user's point of view;

Relationship:

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

(2) Include relationship:

Indicates that a contains B; For example, A is a management data, B can be added data, delete data, etc.

(3) Extended relationship:

D is extended by C, D contains new features, such as D is the query data, C can be printed data, that is, users can query but not print data, printing data is only an extension function.

use case Description template

According to the system boundary, the use case model describes the input and output of the system, determines the participants outside the system, describes the main functions of the system through the use case, describes the interaction between the external participants and the system, and depicts the system as a black box, depicting the functions that the system needs to provide from the user's point of view. Use cases: Case name actor: Participant precondition: Preconditions, that is, the condition that executes this use case must be satisfied postcondition: The post condition, if executed successfully, will certainly become the state of Main flow:1. The user starts session 2. User input Information 3. System Verification and Feedback 4. User repeats 2, 3 steps extensions:3a: Invalid data 1. Error in System prompt