COMP1531

7.2 - SDLC Requirements - Use Cases

Use cases

• Represent a dialogue between the user and the system, with the aim of helping the user achieve a business goal
• The user initiates actions and the system responds with reactions
• They consider the system a black box

Example

Representations

• Informal list of steps
• Use-Case diagrams
• Cockburn style (not required reading)

Initial template

• Use Case: <the name should be the goal as a short active verb phrase>
• Goal in Context: <a longer statement of the goal, if needed>
• Scope: <what system is being considered black-box under design>
• Level: <one of: Summary, Primary task, Subfunction>
• Preconditions: <what we expect is already the state of the world>
• Success End Condition: <the state of the world upon successful completion>
• Failed End Condition: <the state of the world if goal abandoned>
• Primary Actor: <a role name for the primary actor, or description>
• Trigger: <the action upon the system that starts the use case, may be time event>

ATM Example

• Use Case: Withdraw Money
• Goal in Context: Customers need to withdraw money from their accounts without entering the bank
• Scope: ATM, banking infrastructure
• Level: Primary Task
• Preconditions: The customer has an account with the bank
• Success End Condition: The customer has the money they needed to withdraw
• Failed End Condition: The customer has no money
• Primary Actor: Customer
• Trigger: Customer puts card into ATM

Steps taken

MAIN SUCCESS SCENARIO

<put here the steps of the scenario from trigger to goal delivery, and any cleanup after>

<step #> <action description>

ATM Example

In More Depth

• Can be used to model variations in steps (e.g. Insufficient funds)
• If you wish to know more about use cases, see here:
  • Software Engineering - Ivan Marsic (Chapter 2, Section 4)
  • http://www.cs.otago.ac.nz/coursework/cosc461/uctempla.htm
  • Writing Effective Use Cases - Alistair Cockburn