Use Case: A description of a set of sequences of actions, including variants, that a system performs to yield an observable result of value to an actor.[ 📖 : uml-user-guideThe Unified Modeling Language User Guide, 2e, G Booch, J Rumbaugh, and I Jacobson ]
Actor: An actor (in a use case) is a role played by a user. An actor can be a human or another system. Actors are not part of the system; they reside outside the system.
A use case describes an interaction between the user and the system for a specific functionality of the system.
Example 1: 'transfer money' use case for an online banking system
System: Online Banking System (OBS) Use case: UC23 - Transfer Money Actor: User MSS: 1. User chooses to transfer money. 2. OBS requests for details of the transfer. 3. User enters the requested details. 4. OBS requests for confirmation. 5. User confirms. 6. OBS transfers the money and displays the new account balance. Use case ends.
Extensions: 3a. OBS detects an error in the entered data. 3a1. OBS requests for the correct data. 3a2. User enters new data Steps 3a1-3a2 are repeated until the data entered are correct. Use case resumes from step 4. 3b. User requests to effect the transfer in a future date. 3b1. OBS requests for confirmation. 3b2. User confirms future transfer. Use case ends. *a. At any time, User chooses to cancel the transfer. *a1. OBS requests to confirm the cancellation. *a2. User confirms the cancellation. Use case ends.
Example 2: 'upload file' use case of an LMS
- System: A Learning Management System (LMS)
- Actor: Student
- Use Case: Upload file
- Student requests to upload file
- LMS requests for the file location
- Student specifies the file location
- LMS uploads the file
UML includes a diagram type called use case diagrams that can illustrate use cases of a system visually, providing a visual ‘table of contents’ of the use cases of a system.
In the example on the right, note how use cases are shown as ovals and user roles relevant to each use case are shown as stick figures connected to the corresponding ovals.
Unified Modeling Language (UML) is a graphical notation to describe various aspects of a software system. UML is the brainchild of three software modeling specialists James Rumbaugh, Grady Booch and Ivar Jacobson (also known as the Three Amigos). Each of them has developed their own notation for modeling software systems before joining force to create a unified modeling language (hence, the term ‘Unified’ in UML). UML is currently the de facto modeling notation used in the software industry.
Use cases capture the functional requirements of a system.