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Class diagram inheritance and multiplicity
Diagram Diagrams and tools
Definition
Inheritance is shown by an arrow from the subclass to the superclass. Multiplicity (1, 0..*, 1..*) shows how many objects can be related: a student studies 1 or more subjects; a subject has 0 or more students.
Example: Student ---- 1..* Subject.
Found in: course specifications, 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 or label it in the online drawing tool.
- 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.
Related past questions
- 2025 HSC Q22 (3 marks): Modelling tools The Software Engineering Project (Part A) · 3 marks
- Sample exam Q24 (4 marks): Modelling tools (class diagram) The Software Engineering Project (Part B) · 4 marks
These are the questions the flashcard set links to this term. Open each one and compare your answer with its marking criteria.
Study links
- Flashcard: Class diagram inheritance and multiplicity in Diagrams and Modelling Tools (Years 11 and 12) · study that set
- Memorise: Drawing rules: DFD, structure chart, storyboard, decision tree, class diagram, ERD
How to use it in an answer
A model sentence
Diagram: “Inheritance is shown by an arrow from the subclass to the superclass.” Then apply it: Student ---- 1..* Subject.
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.
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.
- 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
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.
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
- Drawing questions (2025 HSC exam Q22): refine attributes into separate inherited classes; use appropriate class diagram symbols.
- Use the term exactly as the syllabus words it, then link it to the scenario in the question; the 2025 feedback repeatedly rewards using the stimulus.
- Answer the command word: outline gives main points only, explain gives a reason or cause, discuss gives both sides.
Related terms
Same group in the syllabus: Class diagram · Entity relationship diagram (ERD) · Storyboard · Decision tree · Data dictionary · Gantt chart · Process diary (log book) · Wiring diagram · Flowchart · Mainline and subroutines (algorithms)