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764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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> **DRAFT** — under teacher review.
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# Excalidraw Diagram Starters — C02
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1abe81 lisa 2026-04-30 18:17:38
School name → 'The Hamilton and Alexandra College' across all wiki pages Sweep rename of the standard subtitle line on every wiki page (sd/, hub, resources). 25 files affected.
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The Hamilton and Alexandra College · Year 12 · 2026
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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Drawing from scratch each session costs 10–15 minutes of setup time and often produces inconsistent notation across the three diagrams. These Excalidraw starters give you pre-framed skeletons — correct shapes, correct labels — so you can focus on the content, not the canvas.
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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> [!TIP]
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> Start in Excalidraw, **then** practise hand-drawing from your finished version. The Excalidraw skeleton is the *plan*; your hand-drawn version under timed conditions is the *performance*.
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---
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## Watch first (≈3 min)
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{{Video|src=https://www.youtube.com/watch?v=OU83LfTIWn8}}
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*Lvl 99 TechSkillz — beginner Excalidraw tour. Watch for: navigation and shape drawing (0:23), styling (0:38), and library/sharing basics. You only need the first 90 seconds for C02 — the rest is optional polish.*
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764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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---
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## Why consistent notation matters
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All three C02 diagrams use the same cast of external entities. If the entity is named "Student" on your context diagram, it must be named "Student" (not "User" or "Person") on your DFD. Starting from a shared canvas makes this consistency automatic.
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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::: info
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**The 9–10 rule.** The rubric requires *"no errors, inconsistencies or omissions"* across **all three** diagrams. Inconsistent entity names between diagrams is a named inconsistency — even if both diagrams are otherwise correct.
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:::
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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---
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## Getting started in Excalidraw
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Excalidraw is available free at [excalidraw.com](https://excalidraw.com). No account required. Your teacher may share a `.excalidraw` file directly — open it with File → Open.
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---
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## Skeleton: Context Diagram
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The context diagram has **exactly one system circle**. Everything else is an external entity (rectangle) or a data flow (labelled arrow).
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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```mermaid
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flowchart LR
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A[Entity A]
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B[Entity B]
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C[Entity C]
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S(("Your System<br/>Name"))
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A -->|labelled flow| S
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S -->|labelled flow| B
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C -->|labelled flow| S
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S -->|labelled flow| C
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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```
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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**Shape key**
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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| Shape | What it represents |
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|---|---|
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| Rectangle | External entity (a person, organisation, or external system) |
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| Circle / oval | The entire system — one only |
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| Labelled arrow | Data flow — must carry a specific name (not "data" or "info") |
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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::: warning
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**Common setup errors to avoid before you start drawing**
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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- Do not add a second circle — multiple circles make it a DFD, not a context diagram.
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- Do not add data stores (double-line rectangles) — they do not exist at context level.
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- Label every arrow with the specific data exchanged, not a direction. Wrong: *"sends data"*. Right: *"assignment submission form"*.
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:::
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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---
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## Skeleton: Level-1 Data Flow Diagram
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The Level-1 DFD **decomposes** the single system circle into 3–6 numbered processes. Use the same external entities as your context diagram.
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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```mermaid
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flowchart LR
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A[Entity A]
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B[Entity B]
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P1((1. Process<br/>Name))
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P2((2. Process<br/>Name))
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P3((3. Process<br/>Name))
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DS[("Data Store")]
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A -->|input| P1
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P1 -->|store| DS
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DS -->|retrieve| P2
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P2 -->|output| B
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P2 --> P3
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P3 -->|update| DS
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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```
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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**Shape key**
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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| Shape | What it represents |
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|---|---|
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| Rectangle | External entity — same names as context diagram |
870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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| Circle / oval | A numbered process (verb–noun phrase, e.g. *"1. Verify Login"*) |
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| Cylinder / double-rectangle | Data store (named collection of stored data) |
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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| Labelled arrow | Data flow |
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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::: success
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**Minimum check before you submit your DFD**
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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- Each process has at least one input AND one output arrow.
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- At least one data store is present.
870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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- Every entity name matches your context diagram **exactly**.
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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- No entity ↔ entity arrows (all flows route through a process).
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- No entity ↔ data store arrows (data stores only connect to processes).
870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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:::
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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---
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## Skeleton: Use Case Diagram
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The use case diagram shows **who** can do **what** with your system. Actors (stick figures) sit outside the system boundary; use cases (ovals) sit inside.
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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```mermaid
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flowchart LR
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A1(["👤 Actor A"])
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A2(["👤 Actor B"])
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subgraph SB["The System"]
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UC1((Use Case 1))
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UC2((Use Case 2))
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UC3((Use Case 3))
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UC4((Use Case 4))
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end
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A1 --- UC1
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A1 --- UC3
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A2 --- UC2
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UC1 -.->|«include»| UC2
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UC4 -.->|«extend»| UC3
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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```
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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**Shape key**
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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| Shape | What it represents |
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|---|---|
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| Stick figure (outside box) | Actor (a person or external system that uses the system) |
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| Oval (inside box) | Use case (a function the system performs) |
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| Rectangle | System boundary |
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| Solid line | Association (actor participates in use case) |
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| Dashed arrow «include» | Use case A *always* triggers use case B |
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| Dashed arrow «extend» | Use case B *sometimes* triggers optional use case C |
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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::: danger
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**Arrow direction rules (the most common exam mistake)**
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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- **«include»:** arrow points FROM the base use case TO the included use case. *(Login includes Verify Credentials → arrow: Login → Verify Credentials.)*
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- **«extend»:** arrow points FROM the extending use case TO the base use case. *(Display Error Message extends Login → arrow: Display Error Message → Login.)*
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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**Rule of thumb:** the arrow always points *towards* the use case that is being **used** or **extended into**.
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:::
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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## Practice check — before the hand-drawn validation
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870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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::: success
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**Run through this list with your Excalidraw diagrams before the timed hand-drawing session**
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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- [ ] Context diagram: exactly one system circle, no data stores, every arrow labelled.
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- [ ] DFD: 3–6 numbered processes, at least one data store, entity names match context diagram.
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- [ ] Use case diagram: all actors outside the boundary, all use cases inside, «include»/«extend» arrows pointing the correct direction.
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- [ ] All three diagrams use identical names for the same entities and data stores.
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If you can redraw all three from memory using only these skeletons as a prompt, you are ready for the hand-drawn validation.
870ff1 lisa 2026-04-27 21:04:13
Excalidraw Starters: add Excalidraw video, mermaid skeletons, blocks - Embed Lvl 99 TechSkillz beginner Excalidraw video (3 min) as Watch first - Replace ASCII context/DFD/UCD skeletons with mermaid (cylinder data store, subgraph for system boundary on UCD) - TIP near top reframes Excalidraw as plan vs hand-draw as performance - INFO callout for the 9-10 cross-diagram-consistency rubric stake - WARNING wraps context-diagram setup errors - SUCCESS wraps DFD minimum-check and final practice-check checklists - DANGER wraps UCD arrow-direction rules (most common exam mistake)
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:::
764b19 lisa 2026-04-26 08:07:23
Source material C02-C05: 6 new DRAFT pages, verified external rows YouTube-first priority sourcing per CXX-WIKI-VIDEO-guide §7. All external resources verified rigorously (oEmbed for YouTube, browser DOM check via playwright-cli for Isaac CS); no curl-200-only links. New DRAFT wiki pages (6): - C02: Excalidraw Diagram Starters - C03: Analytical Tools Template Guide - C04: Efficiency vs Effectiveness; Evaluation Criteria and the SRS - C05: Annotated Mock-up in Excalidraw; Plan B Contingency Table Verified external rows added across CXX-Resources.md (MPT YouTube, NNgroup, VCAA Teaching and Learning, Isaac CS prog_cwk_evaluation_ocr, Ryan's Tutorials). 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) — what can appear on each diagram; the most common notation errors
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- [What Is an Entity?](/sd/C02/What%20Is%20an%20Entity) — human and non-human entities; how to find all entities from your user stories
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- C02 Resources: [external reading and videos](/sd/Resources/C02-Resources)
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