System analysis and Design learning notes (ii) use case model

Use Cases

Using case is a very important concept in system analysis and design, and use cases are a central part of the entire software development process. A use case is an abstract description of a set of action sequences that the system executes and produces corresponding results. These results are either fed back to the participant or as a parameter to other use cases. use case ≠ use case diagram

A use case is a textual description of a series of successful or failed scenarios in which a user uses a system to achieve a particular goal.
The use case diagram gives an image display of the system context, such as the boundary of the system, the internal and external parts of the system. Simple example use case
system under Design (SuD): Telephone system
goal: Talking to the called party
actor: Calling party (primary), called Party billing system (supporting) operator
primary Scenario: Dial, System establish connection, back call tone system connection complete, cancel call tone and call party call hanging machine, system stitches
alternate scenario: Busy dialing, System establishment connection, back busy signal hang machine, system stitches
alternate Scenario: Number does not exist use case diagram
use case Description Concrete component elements

The use case description is divided into three levels:
1. Brief Profile Level
A streamlined generalization that mainly includes the main success scenario.
2. Casual Simple class
Multi-segment description, covering several scenarios.
3. Fully Full Level
Describe every step and possibility of each scene in detail from the details.

A complete use case description can include the following aspects:
* Use cases name Case name
* Scope scope
* Level use case levels
* Primary actor Main participant
* Stakeholders and interests followers and points of concern
* Preconditions pre-conditions
* Success Guarantee the necessary conditions for success
* Main Success Scenario Major success scenarios
* Extensions selectable scenes or failed scenarios
* Special Requirement Special Needs
* Technology and data variations List input and output related information and format
* Frequency of occurrence time frequency
* Miscellaneous Open topic Use case diagram Basic components

Actor actor

Use cases
subsystem Subsystem
Relationship

The associated arrow points to the subject of the information.
Generalization is simply an inheritance relationship, and the child use case points to the parent use case.
Inclusion refers to a complex use case that can be decomposed into several small use cases.
Expansion refers to the extension of the use case function, which is equivalent to additional functionality.