Use Case Diagrams


Use-case diagrams shows interaction between a user (human or machine) and the system.
Use case diagrams describe the functionality of the new system that you are going build.

Notations

Actor: An actor typically represents a user or another system that will interact with the system.
Use case: Use case is a set of scenarios that complete a task. One Use case can include or extend to another Use case
Association: Relations between an actor and a Use case and a Use case if self.
Boundary: Is a scope boundary of the set of use cases

When to use?

Use cases should be used in analysis phase, requirements gathering & analysis and project planning.
For domain modeling.

Who develops it?

Domain Experts.
Analysts.
Developers.

Example:

Following example shows patient appointment booking functionality.

Further readings:

Writing Effective Use Cases -- Alistair Cockburn
UML Distilled -- Martine Fowler
The Unified Modeling Language User Guide --Grady Booch , James Rumbaugh , Ivar Jacobson

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