Relationship in the use case diagram

The use case diagram in UML describes user requirements, describes system functions from the user's perspective, and points out the executors of various functions, emphasizing who is using the system and what functions the system executors are performing. It is mainly used in the requirement analysis stage to describe the functional requirements of the system to be developed.

Link:

There are five relationships in the use case diagram: Association, generalization, inclusion, expansion, and dependency. That is:

Association ):

Communication between participants and use cases. Any Party can send or accept information.

Arrow pointing to Message Receiver

Generalization (inheritance ):

Also known as inheritance relationships, child use cases are similar to parent use cases, but show more special behaviors. Child use cases inherit all structures, behaviors, and relationships of parent use cases. A sub-use case can be a behavior of a parent case or be overloaded.

Arrow pointing to parent use case

Include ):

It is used to break down the Functions Represented by a complex use case into smaller steps.

[Arrow pointing] decomposed functional use cases

Extended (extend ):

It refers to the extension of the use case function, which is equivalent to providing an additional function for the basic use case.

Arrow pointing: Basic use case

Dependency ):

[Arrow to] dependent items

Include, extended, and inheritance:

1. subcases in generalization and included cases occur unconditionally, while extended use cases in extension are conditional.

2. Use Cases are used to provide services for the role (actor). They are provided directly and indirectly. Extended use cases and extended use cases in generalization provide direct services for the role, the included use cases provide indirect services for the role.

3. for extension, it does not include the basic Use Case content, and the basic Use Case content is not extended. For generalization, A subuse case contains all the content of the basic use case.