2026-04-28 16:18:08lisa:
C02: add OtterWiki blocks to remaining 3 pages for visual rhythm
Brings the rest of /sd/C02 in line with Context Diagram, Data Collection
Methods, and Excalidraw Starters (which already use blocks).
CD vs DFD:
- TIP at top: count-the-circles quick test
- DANGER blocks wrap each 'common mistakes' section (CD + DFD)
- SUCCESS block for the mental check before submit
- INFO block for the rubric stake (Why VCAA cares)
Explaining vs Describing:
- TIP at top: circle every 'because' in your plan
- SUCCESS block highlights the explaining-sentence formula
- DANGER block wraps the common traps
- INFO block for Why VCAA cares (examiner-asks-follow-up framing)
What Is an Entity:
- TIP at top: only-people = missed half
- SUCCESS block for the 3-question entity test
- DANGER block wraps commonly-missed-entities table
- INFO block for Why VCAA cares (5-6 vs 9-10 omissions)
sd/C02/Context Diagram vs Data Flow Diagram.md ..
@@ 6,6 6,9 @@
One of the most common errors in C2-2 is treating these two diagrams as interchangeable — or producing a second context diagram and calling it a DFD. They are different levels of the same model, and each has strict rules about what can appear on it.
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> [!TIP]
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> **Quick test:** count the circles. *One* circle = context diagram (Level 0). *Multiple* numbered circles = DFD (Level 1). If you have two circles on a "context diagram", you've drifted into DFD territory.
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---
## Watch first (≈8 min)
@@ 33,36 36,43 @@
## The most common mistakes
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### On the context diagram
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::: danger
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**On the context diagram**
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- **Showing internal processes** (e.g. drawing "Verify User" or "Save Data" as separate circles). If you have more than one circle, you have drawn a DFD, not a context diagram.
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- **Showing internal processes** (e.g. drawing *"Verify User"* or *"Save Data"* as separate circles). If you have more than one circle, you have drawn a DFD, not a context diagram.
- **Showing a data store** (the double-line rectangle). Data stores do not exist at context-diagram level — the whole system is one black box.
- **Connecting entities to each other** with arrows. Every arrow must touch the system circle.
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:::
-
### On the Level-1 DFD
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::: danger
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**On the Level-1 DFD**
- **Drawing only one process circle** — that is a context diagram in disguise. Decompose the system into its major functions (3–6 processes).
- **Missing data stores** — if your software saves anything (user accounts, records, preferences), you need at least one data store.
- **Inconsistent entities** — your DFD entities must be identical names and roles to your context diagram entities. Divergence is a rubric error.
- **A process with only inputs and no outputs** (or only outputs) — a process that transforms nothing is not a process.
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:::
---
## A mental check before you submit
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::: success
Ask yourself for each diagram:
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**Context diagram:** "If I covered the label on the system circle, would a reader know this is one system, not a set of functions?" If you have multiple circles, it fails this check.
-
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**DFD:** "Can I trace a path — from an external entity, through at least two processes and one data store, to an output?" If not, your decomposition is incomplete.
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- **Context diagram:** *"If I covered the label on the system circle, would a reader know this is one system, not a set of functions?"* — If you have multiple circles, it fails this check.
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- **DFD:** *"Can I trace a path — from an external entity, through at least two processes and one data store, to an output?"* — If not, your decomposition is incomplete.
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:::
---
-
## Why VCAA cares
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::: info
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**Why VCAA cares**
The C2-2 rubric at **3–4** requires *"illustrates the features of the context diagram/s"*. The marker is checking: one system circle, correct entities, labelled flows. Drawing internal processes on the context diagram is a notation error that costs marks at every level above 3–4.
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At **9–10**, the rubric requires *"no errors, inconsistencies or omissions"* across all three diagrams. Inconsistent entities between context and DFD is an inconsistency — even if both diagrams are otherwise correct.
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At **9–10**, the rubric requires *"no errors, inconsistencies or omissions"* across **all three diagrams**. Inconsistent entities between context and DFD is an inconsistency — even if both diagrams are otherwise correct.
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:::
---
sd/C02/Explaining vs Describing Your Data Collection.md ..
@@ 6,6 6,9 @@
The jump from 7–8 to 9–10 on Indicator 1 (Data Collection) comes down to a single word in the rubric: **"explains"** instead of **"describes"**. Every year, students hit 7–8 and can't understand why — it is almost always this.
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> [!TIP]
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> Read your `data-collection-plan.md` and circle every sentence that contains the word *"because"*. If there are fewer than three, you are *describing*, not *explaining* — and you will cap at 7–8 regardless of how thorough the plan is.
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---
## The rubric in plain language
@@ 39,25 42,31 @@
## The formula for an "explaining" sentence
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::: success
> I chose **[method]** over **[alternative method]** because I needed **[type of data / depth / scale]**, and **[method]** allows me to **[specific advantage]**.
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Write one of these for each of your three or more data collection methods. If you can't complete the sentence, you do not yet know why you chose that method — and the examiner will ask.
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Write one of these for **each** of your three or more data collection methods. If you can't complete the sentence, you do not yet know why you chose that method — and the examiner will ask.
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:::
---
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## Common traps
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::: danger
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**Common traps**
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- **"I used interviews because they are good for qualitative data."** — This is still describing (a general property of interviews), not explaining your specific choice. Add: *why did this project need qualitative data at this stage?*
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- **"I chose three methods to get a variety of data."** — "Variety" is not a reason. Name what each method adds that the others cannot.
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- **"I used surveys because they are easy to send out."** — Convenience is not a justification the rubric rewards. Reframe it: *a survey allowed me to reach all 80 students in the year level simultaneously, which an interview schedule could not achieve within the one-week collection window.*
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- **"I used interviews because they are good for qualitative data."** — Still describing (a general property of interviews), not explaining your specific choice. Add: *why did this project need qualitative data at this stage?*
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- **"I chose three methods to get a variety of data."** — *"Variety"* is not a reason. Name what each method adds that the others cannot.
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- **"I used surveys because they are easy to send out."** — Convenience is not a justification the rubric rewards. Reframe: *a survey allowed me to reach all 80 students in the year level simultaneously, which an interview schedule could not achieve within the one-week collection window.*
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:::
---
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## Why VCAA cares
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::: info
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**Why VCAA cares**
-
The C2-1 validation is a **presentation** — the examiner will ask follow-up questions. A student who has only described their methods will struggle to answer "Why didn't you just use a survey for everything?" A student who has explained their choices has already answered that question in their own plan.
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The C2-1 validation is a **presentation** — the examiner will ask follow-up questions. A student who has only described their methods will struggle to answer *"Why didn't you just use a survey for everything?"*. A student who has explained their choices has already answered that question in their own plan.
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Practise saying your explanations out loud before the validation. If you stumble, rewrite. The rubric rewards understanding, not recall.
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Practise saying your explanations *out loud* before the validation. If you stumble, rewrite. The rubric rewards understanding, not recall.
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:::
---
sd/C02/What Is an Entity.md ..
@@ 4,7 4,10 @@
Hamilton College · Year 12 · 2026
-
On context diagrams and data flow diagrams, students frequently draw only the humans they can think of — "Student", "Teacher" — and miss every external system their software talks to. Missing an entity is a rubric error at every level above 3–4, because the rubric rewards *"relationships between the existing system, entities and data flows"*.
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On context diagrams and data flow diagrams, students frequently draw only the humans they can think of — *"Student"*, *"Teacher"* — and miss every external system their software talks to. Missing an entity is a rubric error at every level above 3–4, because the rubric rewards *"relationships between the existing system, entities and data flows"*.
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+
> [!TIP]
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> If your context diagram only has *people* as entities, you've almost certainly missed half of them. Every login, every email, every external API your project touches is its own entity.
---
@@ 29,28 32,33 @@
## A quick test: is it an entity?
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::: success
Ask three questions:
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1. Does it send data **into** my system, or receive data **out** of it?
2. Is it **outside** the boundary of the software I am building?
3. Is it a **distinct role or system** (not an internal component of my software)?
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If all three answers are "yes" — it is an entity. Add it to your diagram.
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If all three answers are *"yes"* — it is an entity. Add it to your diagram.
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If it is *inside* your system (e.g. a function you are writing, a class in your code, a database table your code owns) — it is **not** an entity. It belongs on the DFD as a process or data store.
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If it is *inside* your system (a function you are writing, a class in your code, a database table your code owns) — it is **not** an entity. It belongs on the DFD as a process or data store.
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:::
---
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## Common omissions from student context diagrams
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::: danger
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**Commonly missed entities — by project type**
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These are the entities students most often miss, sorted by project type:
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These are the entities students most often miss. Check whether *any* apply to your project before submitting.
| Project type | Commonly missed entity | Why it is missed |
|---|---|---|
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| Any project with login | Authentication provider (e.g. Google OAuth) | Students think login is "inside" their app |
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| Any project with login | Authentication provider (e.g. Google OAuth) | Students think login is *"inside"* their app |
| Any project that emails users | Email server / SMTP service | Students don't model outgoing system calls |
| School management tool | Admin user or IT department | Students only think about the primary user |
| App using external data | External database or API (e.g. weather API) | Students model the API as a feature, not an entity |
| App with notifications | Push notification service | Treated as internal, but it is external |
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:::
---
@@ 65,11 73,13 @@
---
-
## Why VCAA cares
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::: info
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**Why VCAA cares**
-
The C2-2 rubric at **5–6** requires *"illustrates the relationships between the existing system, entities and data flows"*. "Some errors or omissions exist" is still acceptable at 5–6. But at **9–10**, "no errors, inconsistencies or omissions exist" — a missing entity is an omission, and omissions cost you the top band.
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The C2-2 rubric at **5–6** requires *"illustrates the relationships between the existing system, entities and data flows"*. *"Some errors or omissions exist"* is still acceptable at 5–6. But at **9–10**, *"no errors, inconsistencies or omissions exist"* — a missing entity **is** an omission, and omissions cost you the top band.
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The most common C2-2 omission flagged in past years: the email server or notification service that every project needs but few students draw.
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The most common C2-2 omission flagged in past years: the **email server or notification service** that every project needs but few students draw.
