Commit 9287c9

2026-04-27 20:34:08 lisa: Context Diagram: add click-to-reveal answers in Self-check Use OtterWiki spoiler blocks (>!) so students attempt each MCQ before revealing the answer + a one-sentence rationale.

sd/C02/Context Diagram.md ..
@@ 107,16 107,22 @@
	## Self-check
-	Test yourself before moving on. Answers in your notes, not on the page.
+	Test yourself before moving on. Answer in your head first, then click the spoiler to check.
-	1. Which of these is **not** a component of a context diagram?
-	*(a) process · (b) entity · (c) data flow · (d) data store*
+	**1.** Which of these is **not** a component of a context diagram?
+	*(a) process · (b) entity · (c) data flow · (d) data store*
-	2. In a context diagram, which statement is correct?
-	*(a) Entities can connect directly to other entities · (b) Data flows can only connect entities to the system process · (c) Multiple processes can be shown · (d) All flows must be unidirectional*
+	>! **(d) data store.** Data stores belong on the Level-1 DFD, not the context diagram. At Level 0 the whole system is a single black box — its internal storage is hidden.
-	3. You're drawing a context diagram for a Library Management System. How should *"borrowing a book"* appear?
-	*(a) An entity labelled "Borrowing" · (b) A process inside the system · (c) A data flow labelled "Book borrowing request" from Borrower to the system · (d) A rectangle showing the book collection*
+	**2.** In a context diagram, which statement is correct?
+	*(a) Entities can connect directly to other entities · (b) Data flows can only connect entities to the system process · (c) Multiple processes can be shown · (d) All flows must be unidirectional*
+
+	>! **(b) Data flows can only connect entities to the system process.** Every arrow must touch the system circle. Entity↔entity flows are never allowed; (c) describes a DFD, not a context diagram; (d) is false — a flow can be bidirectional if data moves both ways.
+
+	**3.** You're drawing a context diagram for a Library Management System. How should *"borrowing a book"* appear?
+	*(a) An entity labelled "Borrowing" · (b) A process inside the system · (c) A data flow labelled "Book borrowing request" from Borrower to the system · (d) A rectangle showing the book collection*
+
+	>! **(c) A data flow labelled "Book borrowing request" from Borrower to the system.** Borrowing is an *action*, not an entity or a thing. On a context diagram, actions surface as labelled data flows. (b) would be a process — but the context diagram has only one process (the whole system).
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