Class diagram

Diagram Diagrams and tools

Definition

A visual representation of an object-oriented system: classes (name, attributes, methods) and the relationships between them.

Example: Person with Student and Parent inheriting from it.

Found in: syllabus, course specifications, 2025 HSC marking guidelines, sample exam and familiarisation guidelines, school notes.

Where it is used in the test

Syllabus area: Diagrams and tools.

Question types it can appear in

Drawing: Draw a class diagram with inheritance (2025 Q22, sample Q24)
Short answer: Define, outline or explain it and tie it to the scenario.
Multiple choice: Pick the option that matches the definition or example.

Where it has appeared in the paper

The Software Engineering Project (Part A, B). Part letters follow each paper’s own layout.

Study links

Flashcard: Class diagram in Diagrams and Modelling Tools (Years 11 and 12) · study that set
Memorise: Drawing rules: DFD, structure chart, storyboard, decision tree, class diagram, ERD
Notes: Part 3. Where this has been examined (see ../../question_bank.md) (The Software Engineering Project (Year 12))
Notes: Part 3. Where this has been examined (see ../../question_bank.md) (Pseudocode, flowcharts and diagram rules)
Notes: Modelling tools: DFD, structure charts, storyboards, flowcharts, class diagrams (The Software Engineering Project (Year 12))
Notes: Drawing rules: DFD, structure chart, storyboard, decision tree, class diagram, ERD (Pseudocode, flowcharts and diagram rules)

How to use it in an answer

A model sentence

General advice, built from the definition and example above

Diagram: “A visual representation of an object-oriented system: classes (name, attributes, methods) and the relationships between them.” Then apply it: Person with Student and Parent inheriting from it.

In a short answer, give the definition in your own words first, then tie it to the situation in the question. Do not copy the example above unless it fits the scenario.

Command words used with it

General advice

No linked question shows the command word for this term. Across the past drawing and short answer questions in this bank the words used most are: Explain, Outline, Describe, Compare, Classify, Analyse. Check the actual word in your question.

Technique for the question types

Drawing: Use the online drawing tool: label every symbol and arrow, use the correct symbols from the specification, and add every required item.
Short answer: One clear point per mark, use the stimulus and course terms, and answer the command word.
Multiple choice: Read all four options, rule out wrong ones, pick one; no penalty for guessing so never leave blank.

What the marking guidelines and feedback say

2025 HSC Q22 (3 marks): Modelling tools

Technique: move attributes shared by several classes up into a parent (superclass) and draw an inheritance arrow from each subclass to the parent; leave only unique attributes in subclasses. Marker feedback: refine attributes into separate inherited classes; use appropriate class diagram symbols.

Sample exam Q24 (4 marks): Modelling tools (class diagram)

A reasoned design (NOT the NESA diagram): classes Trip(tripID; assignTicket()), PassengerCar(carModelCode), Engine(engineModelCode), Area(areaType, numSeats) with subclasses Executive (20 seats) and Standard (400 seats), Passenger(email, phone; buyTicket()) with subclass FrequentTraveller(loyalty info), Ticket(ticketType, seatNumber). Relationships: Trip 1 to many PassengerCar; Trip 1 to 1 Engine; Trip 1 to 2 Area; Passenger 1 to 0..* Ticket; Ticket * to 1 Trip. Show multiplicities and inheritance arrows (hollow triangle).

Common mistakes

Marker feedback on other questions of the same type (code and diagram feedback often applies across questions)

Drawing questions (2025 HSC exam Q22): refine attributes into separate inherited classes; use appropriate class diagram symbols.