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2026-06-08 11:36:12 lisa: C05: add Object Descriptions & Class Diagrams page (5th design tool) Class diagram (Animal example) + notation key, properties/methods/events incl. GUI events, links to data dictionary (attributes) and pseudocode (methods, Level 9). Added to home index under C5-1 and cross-linked from pseudocode page. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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- [Data Dictionary — Format is not Type](/sd/C05/Data%20Dictionary%20-%20Format%20is%20not%20Type) — the most common data-dictionary error: the Format column is a storage/display pattern, not a synonym for data type
- [IPO Charts — Process Means Steps](/sd/C05/IPO%20Charts%20-%20Process%20Means%20Steps) — why the Process column must be numbered algorithm steps, not a label for the output
- [VCAA Pseudocode — Not Python](/sd/C05/VCAA%20Pseudocode%20Not%20Python) — write language-independent Structured English (`←`, `<>`, `ENDIF`), not Python-flavoured pseudocode
+- [Object Descriptions and Class Diagrams](/sd/C05/Object%20Descriptions%20and%20Class%20Diagrams) — the fifth design tool for OOP projects: a class's properties, methods and events, and how to read a class diagram (Level 7–9)
## C5-2 — Design principles & UX
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+> **DRAFT** — under teacher review.
+
+# Object Descriptions and Class Diagrams
+
+The Hamilton and Alexandra College · Year 12 · 2026
+
+If your solution uses **objects and classes**, the fifth design tool is the **object description**. VCAA defines it as a tool that *"describes all of the relevant properties, methods and events in an object or class."* A **class diagram** is the standard way to draw a whole set of object descriptions at once and show how the classes relate.
+
+This is a **Level 7+** tool in C5-1, and at **Level 9** you are also expected to write pseudocode for the methods inside your classes.
+
+> [!NOTE]
+> **Only if you use OOP.** If your solution genuinely does not use classes and objects, you do not need object descriptions. But most SAT projects of any real size have at least a few classes — and a class diagram is the clearest way to show them.
+
+---
+
+## Reading a class diagram
+
+Each box is a **class**. The top section lists its **attributes** (properties), the bottom section lists its **methods** (actions), and the arrows show **relationships** between classes.
+
+```mermaid
+---
+title: Animal example
+---
+classDiagram
+ note "From Duck till Zebra"
+ Animal <|-- Duck
+ note for Duck "can fly<br>can swim<br>can dive<br>can help in debugging"
+ Animal <|-- Fish
+ Animal <|-- Zebra
+ Animal : +int age
+ Animal : +String gender
+ Animal: +isMammal()
+ Animal: +mate()
+ class Duck{
+ +String beakColor
+ +swim()
+ +quack()
+ }
+ class Fish{
+ -int sizeInFeet
+ -canEat()
+ }
+ class Zebra{
+ +bool is_wild
+ +run()
+ }
+```
+
+Read it like this: `Animal` is the **base class**. `Duck`, `Fish` and `Zebra` are all *a kind of* Animal, so each one **inherits** Animal's attributes (`age`, `gender`) and methods (`isMammal()`, `mate()`) and then adds its own. `Duck` adds `beakColor`, `swim()` and `quack()`; it doesn't have to redefine `age` because it already has it from `Animal`.
+
+---
+
+## The notation you need
+
+| Symbol | Meaning |
+|---|---|
+| `+` | **Public** — usable from outside the class |
+| `-` | **Private** — usable only inside the class |
+| `age : int` | An **attribute** and its **data type** |
+| `isMammal()` | A **method** (an action the object can perform) |
+| `isUpcoming() : bool` | A method and its **return type** |
+| `Animal <|-- Duck` | **Inheritance** — "Duck *is a* Animal" |
+
+> [!TIP]
+> Every attribute should have a **data type** and every method should show its **parameters and return type**. "`age`" alone is weak; "`+ age : int`" is design-ready. This is exactly the precision that lifts C5-1 from the middle bands into 7–9.
+
+---
+
+## Properties, methods — *and events*
+
+A class diagram shows properties and methods well. But VCAA object descriptions also include **events** — especially for **GUI objects** (buttons, text fields, menus). An event is something the object *responds to*, like a click.
+
+For a login button you might describe the object like this:
+
+| Aspect | Example for `btnLogin` (a button) |
+|---|---|
+| **Properties** | `caption` = "Log in", `enabled` = true |
+| **Methods** | `setEnabled(state)` |
+| **Events** | `onClick` → runs the *Validate User* process |
+
+So: the class diagram carries your properties and methods; for interface objects, add a short note or table documenting the **events** as well.
+
+---
+
+## How it connects to your other design tools
+
+The object description is not an island — it ties the whole detailed design together:
+
+- **Properties ↔ data dictionary.** Every attribute is a field. `studentID : int` becomes a data-dictionary row with a type, size and format. See [Data Dictionary — Format is not Type](/sd/C05/Data%20Dictionary%20-%20Format%20is%20not%20Type).
+- **Methods ↔ pseudocode.** At Level 9 you write pseudocode for each method. The `is_passing()` example on the pseudocode page is exactly a method from a class diagram, written out. See [VCAA Pseudocode — Not Python](/sd/C05/VCAA%20Pseudocode%20Not%20Python).
+- **Classes ↔ mock-ups and IPO charts.** The objects are what sit *behind* your screens and processes.
+
+---
+
+## Common mistakes
+
+### Mistake 1: An object description with no methods
+
+> ~~A box listing only attributes~~
+
+That is just a data dictionary in disguise. An object description must include the **methods** (and, for GUI objects, the **events**) — that is what makes it an *object*.
+
+### Mistake 2: No visibility or data types
+
+> ~~`beakColor`, `swim`~~
+
+Show whether each member is public (`+`) or private (`-`), give every attribute a **type**, and give every method its **parameters and return type**.
+
+### Mistake 3: Classes drawn with no relationships
+
+If `Teacher` is a kind of `Student`, draw the inheritance arrow. A diagram of disconnected boxes hides the design thinking the arrows are meant to show.
+
+### Mistake 4 (Level 9): A class diagram but no method pseudocode
+
+At Level 9 the methods in your diagram must be backed by pseudocode. A diagram on its own caps you below the top band.
+
+---
+
+## Check Your Understanding
+
+1. In the Animal diagram, name two things `Duck` inherits from `Animal`, and one thing `Duck` adds of its own.
+
+>| **Inherits** (any two): `age`, `gender`, `isMammal()`, `mate()`. **Adds** (any one): `beakColor`, `swim()`, `quack()`.
+
+2. What do `+` and `-` mean in front of an attribute or method?
+
+>| `+` means **public** (accessible from outside the class); `-` means **private** (accessible only inside the class).
+
+3. Which design tool turns the *methods* in your class diagram into step-by-step logic — and at which level is it required?
+
+>| **Pseudocode**, required at **Level 9** (pseudocode for the functions and methods within your classes). See [VCAA Pseudocode — Not Python](/sd/C05/VCAA%20Pseudocode%20Not%20Python).
+
+---
+
+## Credits
+
+- Class-diagram example adapted from the [Mermaid](https://mermaid.js.org/) documentation's *Animal* sample.
+
+---
+
+## See also
+
+- [VCAA Pseudocode — Not Python](/sd/C05/VCAA%20Pseudocode%20Not%20Python) — write the pseudocode for each method (Level 9)
+- [Data Dictionary — Format is not Type](/sd/C05/Data%20Dictionary%20-%20Format%20is%20not%20Type) — each attribute is a data-dictionary field
+- [Sketch vs Mock-up](/sd/C05/Sketch%20vs%20Mock-up)
+- [C05 Resources](/sd/Resources/C05-Resources)
+
+← Back to [C05 Home](/sd/C05/C05-home) · [VCE Software Development Hub](/sd/VCE%20Software%20Development%20Hub)
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## See also
- [IPO Charts — Process Means Steps](/sd/C05/IPO%20Charts%20-%20Process%20Means%20Steps) — turn an IPO Process column into formal pseudocode
+- [Object Descriptions and Class Diagrams](/sd/C05/Object%20Descriptions%20and%20Class%20Diagrams) — the methods you write pseudocode for come from here
- [C05 Resources](/sd/Resources/C05-Resources)
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