What is Use Case Diagram & Use Cases?

What is Use Case Diagram (UCD) ?

Use Case Diagram (UCD) shows interaction among actors (external parties) and Use Cases (Modules) of the System.It is not Data Flow Diagram.

What is Use Case ?

• Use Cases is detailing of the Use Case Diagram (UCD).
• Use Cases are textual artifacts.
• Use Case depicts functional requirements primarily.

Use Case Diagram for PoS

 

Use Cases Types

• Black-box use cases describe system responsibilities, i.e. define what the system must do.
• Uses cases may be written in three formality types
  • Brief: one-paragraph summary, usually of the main success scenario.
  • Casual: Informal paragraph format (e.g. Handle returns)
  • Fully dressed: elaborate. All steps and variations are written in detail.
• Handle returns
  Main success scenario: A customer arrives at a checkout with items to return. The cashier uses the POS system to record each returned item.
  • Alternate scenarios: If the credit authorization is reject, inform customer and ask for an alternative payment method. If item identifier not found in the system, notify the Cashier and suggest manual entry of the identifier code.

 

Styles of Use Cases

Essential vs. Concrete style

• Essential: Focus is on intend.
  • Avoid making UI decisions
• Concrete: UI decisions are embedded in the use case text.
  • e.g. “Admin enters ID and password in the dialog box (see picture X)”
  • Concrete style not suitable during early requirements analysis work.