← VCE Software Development U3O2

Use case diagram: system boundary and actors

A diagram showing actors (stick figures) outside a system boundary box, linked by lines to the use cases inside the box that they can do with the system.

Part of: VCE Software Development - U3O2 - Analysis and Design — Module 47

Understanding Use case diagram: system boundary and actors in VCE Software Development U3O2

What it does: The customer starts the use case to reach their own goal, which makes them a primary actor. Actors are external to the system, so they sit outside the boundary box. Only the use cases go inside the box. A use case diagram uses simple lines to link actors to use cases. Arrows labelled with data are used in data flow diagrams instead.

Common mistakes: Actors are people or systems outside the system, so they are drawn outside the system boundary box. The line should say (outside box). Actors are drawn as stick figures. Ovals are used for use cases. The line should say (stick figure).

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This module's key terms are also in a printable crossword (Modules 42–51) and word search (Modules 26–51).

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Learning
Duo
Where should actors be drawn in a use case diagram?
Inside the system boundary boxOutside the system boundary box
Matches
A Teacher stick figure drawn inside the system boundary box next to the use cases
↓
Actors must be drawn outside the system boundary. Only use cases go inside the box.
Applying
Meanings
Term
Use case diagram
Meaning
A diagram showing actors (stick figures) outside a system boundary box, linked by lines to the use cases inside the box that they can do with the system.
Practice
System boundary: Library Loan System
Testing
Gaps
Student
Check Answer
Spots
1System: Library App
2Actor: Student (inside box)

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Quick Questions

1. Where should actors be drawn in a use case diagram?
A. Outside the system boundary box ✓
B. Inside the system boundary box
Actors are external to the system, so they sit outside the boundary box. Only the use cases go inside the box.
2. Which symbol is used to represent an actor?
A. A rectangle with rounded corners
B. A stick figure ✓
Actors are drawn as stick figures with their name underneath. Use cases are drawn as ovals inside the boundary.
3. What does the system boundary box show?
A. What is inside the system and what is outside it ✓
B. The order in which tasks are completed
The boundary box separates the use cases the system provides from the actors outside it. It does not show sequence or timing.
4. A student logs into a school library system to borrow a book. How should the student be shown?
A. As a use case inside the boundary
B. As an actor outside the boundary, linked to a use case ✓
The student is a person who uses the system, so they are an actor. 'Borrow book' would be the use case inside the box.
5. Which is a primary actor for an online shop?
A. The customer who places an order ✓
B. The payment gateway that processes the card
A primary actor starts the interaction to achieve a goal, like a customer ordering. The payment gateway is a secondary actor that supports the use case.

Match the Pairs

System boundary (rectangle) → A box drawn around the use cases that marks what is inside the system. Everything outside the box is not part of the system.
Stick figure labelled 'Student' → An actor: a user or role outside the system who interacts with it, drawn as a stick figure beside the boundary box.
A primary actor starts an interaction with the system to achieve their own goal, so they are drawn on the left of the boundary. → Customer -----> (Place Order)
A secondary actor is an external system or person that supports the use case. They are usually drawn on the right of the boundary. → (Process Payment) -----> Payment Gateway
A Teacher stick figure drawn inside the system boundary box next to the use cases → Actors must be drawn outside the system boundary. Only use cases go inside the box.
A system boundary box drawn around only the actors, with the use cases left outside it → The boundary box is the wrong way around. It should surround the use cases, and the actors should be outside it.

Key Term

Use case diagram
A diagram showing actors (stick figures) outside a system boundary box, linked by lines to the use cases inside the box that they can do with the system.

Fill in the Blanks

1. actor Student actor Librarian
Hint: Type the keyword that declares a stick figure outside the system.
2. rectangle "Library System" { usecase "Borrow book" as UC1 }
Hint: Type the keyword that draws the system boundary box around the use cases.
3. rectangle "Library System" { usecase "Borrow book" as UC1 }
Hint: Type the keyword that declares an oval use case inside the system boundary.
4. actor Student usecase "Borrow book" as UC1 Student --> UC1
Hint: Type the name of the primary actor who starts this use case.
5. actor Librarian usecase "Borrow book" as UC1 UC1 --> Librarian
Hint: Type the name of the secondary actor that supports the system, declared on line 1.

Spot the Error

Question 1
A System: Library App
B Actor: Student (inside box)
C Use case: Borrow book (inside)
D Link: Student -- Borrow book
Line B — Actors are people or systems outside the system, so they are drawn outside the system boundary box. The line should say (outside box).
Question 2
A System: Canteen Orders
B Actor: Student (oval)
C Use case: Order lunch (oval)
Line B — Actors are drawn as stick figures. Ovals are used for use cases. The line should say (stick figure).
Question 3
A System: Online Shop
B Primary: Customer (starts)
C Secondary: Bank (starts)
Line C — A secondary actor supports the use case, for example by processing a payment. It does not start it. The primary actor starts it, so it should say (assists).
Question 4
A Boundary box: Librarian
B Actor: Librarian (stick man)
C Use case: Add book (inside)
Line A — The system boundary box is labelled with the name of the system, such as Library System. Librarian is an actor, and actors sit outside the box.
Question 5
A System: Gym Booking
B Primary: Member (stick figure)
C Secondary: Payment system
D Use case: Book class (outside)
E Member -- Book class
Line D — Use cases are the functions of the system, so they are drawn inside the system boundary box. The line should say (inside).

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