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ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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> **DRAFT** — under teacher review.
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# What Is an Entity? (It's Not Just a Person)
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Hamilton College · Year 12 · 2026
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cfcd0d lisa 2026-04-28 16:18:08
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)
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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.
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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---
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## The VCAA definition
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> **Entity** — the users or external systems that interact with the system being created.
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Two words matter: **users** (human roles) and **external systems** (non-human). Both go on your context diagram as rectangles.
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---
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## Types of entity — with examples
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| Type | What it is | VCE SAT examples |
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|---|---|---|
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| **Human user (primary)** | The person the software is primarily built for | Student, Teacher, Administrator |
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| **Human user (secondary)** | A person affected by the system's outputs | Parent, School Principal |
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| **External software system** | An API, platform, or service your system sends data to or receives data from | Google Calendar API, Payment Gateway, Email Server |
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| **External data source** | A data feed or file system outside your application boundary | School database, CSV import, Government open data |
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---
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## A quick test: is it an entity?
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cfcd0d lisa 2026-04-28 16:18:08
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)
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::: success
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Ask three questions:
cfcd0d lisa 2026-04-28 16:18:08
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)
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ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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1. Does it send data **into** my system, or receive data **out** of it?
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2. Is it **outside** the boundary of the software I am building?
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3. Is it a **distinct role or system** (not an internal component of my software)?
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cfcd0d lisa 2026-04-28 16:18:08
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)
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If all three answers are *"yes"* — it is an entity. Add it to your diagram.
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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cfcd0d lisa 2026-04-28 16:18:08
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)
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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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:::
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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---
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cfcd0d lisa 2026-04-28 16:18:08
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)
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::: danger
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**Commonly missed entities — by project type**
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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cfcd0d lisa 2026-04-28 16:18:08
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)
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These are the entities students most often miss. Check whether *any* apply to your project before submitting.
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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| Project type | Commonly missed entity | Why it is missed |
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|---|---|---|
cfcd0d lisa 2026-04-28 16:18:08
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)
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| Any project with login | Authentication provider (e.g. Google OAuth) | Students think login is *"inside"* their app |
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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| Any project that emails users | Email server / SMTP service | Students don't model outgoing system calls |
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| School management tool | Admin user or IT department | Students only think about the primary user |
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| App using external data | External database or API (e.g. weather API) | Students model the API as a feature, not an entity |
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| App with notifications | Push notification service | Treated as internal, but it is external |
cfcd0d lisa 2026-04-28 16:18:08
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)
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:::
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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---
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## User stories → entities: the reliable method
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Your `data-collection-plan.md` user stories are the best source of entities. For each story:
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- **"As a [role]"** → that role is probably an entity (if they interact with your system directly).
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- **"I want [goal] so that [benefit]"** → what external systems does achieving this goal require? Each one is a candidate entity.
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Work through every user story before finalising your context diagram.
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4a5120 lisa 2026-04-28 17:03:38
What Is an Entity: add Gherkin scenarios as optional entity-discovery tool Adds a 'Going further' subsection with the LitheSpeed Gherkin video (~1 min), a Given/When/Then ATM example, and a worked breakdown showing which entities the scenario surfaces. Framed explicitly as not curriculum-required but powerful — the Given preconditions and Then effects force students to name external systems they'd miss from the user story alone.
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### Going further: Gherkin scenarios *(optional but excellent)*
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::: info
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**Not required by the VCAA curriculum** — but a powerful tool for surfacing entities you'd otherwise miss. Worth knowing if you want top-band detail.
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A Gherkin scenario expands a user story into concrete **Given / When / Then** steps. Every noun in those steps is a candidate entity.
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{{Video|src=https://www.youtube.com/watch?v=bxeNxhOSGJg}}
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*LitheSpeed — What Is Gherkin? (~1 min). The bare-bones intro; no need to learn the BDD tooling around it.*
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**Example.** A user story like *"As an account holder I want to withdraw cash so that I have money for the day"* expands to:
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```gherkin
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Feature: Account Holder withdraws cash
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Scenario: Account has sufficient funds
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Given the account balance is $100
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And the card is valid
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And the machine contains enough money
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When the Account Holder requests $20
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Then the ATM should dispense $20
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And the account balance should be $80
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And the card should be returned
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```
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**Entities this scenario surfaces** (each underlined noun is an external system the ATM software talks to):
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- **Account Holder** — the human user (you'd already have this).
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- **Card / Authentication system** — *"the card is valid"* implies an external check (bank network or token validator).
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- **Bank account database** — *"balance is $100 → $80"* means your software reads and writes to an external account store.
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- **Cash dispenser hardware** — *"dispense $20"* is a physical subsystem outside your software.
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- **Card reader hardware** — *"card should be returned"* is another physical subsystem.
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A user story alone might surface only *Account Holder*. The Gherkin expansion forces you to confront every Given precondition and every Then effect — that's where the missing entities live.
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ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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---
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cfcd0d lisa 2026-04-28 16:18:08
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)
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::: info
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**Why VCAA cares**
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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cfcd0d lisa 2026-04-28 16:18:08
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)
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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.
ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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cfcd0d lisa 2026-04-28 16:18:08
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)
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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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ef4237 lisa 2026-04-25 22:18:29
Add C02 wiki content (DRAFT) — landing page, key-concept pages, Resources Builds out C02 (Data Collection & Analytical Diagrams). Adds C02-home, 3 new key-concept pages (DRAFT for teacher review tomorrow), external resource rows in C02-Resources.md, and a Hub link to C02-home. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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## See also
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- [Context Diagram vs Data Flow Diagram](/sd/C02/Context%20Diagram%20vs%20Data%20Flow%20Diagram)
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- C02 Resources: [external reading and videos](/sd/Resources/C02-Resources)
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