← IGCSE Computer Science Paper 2

Structure diagram

A diagram with the whole problem in a top box, joined by lines to lower boxes for each sub-problem, in levels. It shows the parts of the problem, not the order of the steps.

Part of: IGCSE Computer Science 0478 — 7b Decomposition and Sub-systems — Module 21, WA Computer Science ATAR Year 11 — Modular Programming — Module 2

Understanding Structure diagram in IGCSE Computer Science Paper 2

What it does: Ask Question, Check Answer and Show Score are all one level below Quiz Game, so they are on the same level. The boxes show which parts exist. A flowchart or pseudocode is needed to show the order of the steps. The top box names the whole problem. The lower boxes break it into sub-problems. Boxes joined to the same parent sit at the same level. Neither one is a part of the other. Each box stands for a sub-problem of the problem. It is not a line of code. In a structure diagram the highest box always holds the whole problem, here the library system.

Common mistakes: The top box must name the whole problem, not just one part of it. Line 1 should be 'L0: Run a school shop'. 'Check stock' is a sub-problem and belongs at level 1. 'Work out averages' is a sub-problem of the whole app, so it sits at the same level as the other boxes under the top box. It should be 'L1: Work out averages', not level 2.

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This module's key terms are also in a printable crossword (Modules 107–118) and word search (Modules 94–118).

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Learning

Duo

Which box sits at the very top of a structure diagram?

A box naming the last step to be doneA box naming the whole problem

Matches

Level 1: Quiz Game. Level 2: Ask Question, Check Answer. Top box: Ask Question

↓

The top box must name the whole problem, Quiz Game, not one of the sub-problems such as Ask Question.

Applying

Meanings

Term

structure diagram

Meaning

A diagram with the whole problem in a top box, joined by lines to lower boxes for each sub-problem, in levels. It shows the parts of the problem, not the order of the steps.

Practice

Quiz Game

Testing

Gaps

Level : Quiz Game

Check Answer

Spots

1L0: Check stock

2L1: Record sales

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Quick Questions

1. Which box sits at the very top of a structure diagram?

A. A box naming the whole problem ✓

B. A box naming the last step to be done

The top box names the whole problem. The lower boxes break it into sub-problems.

2. What do the lines in a structure diagram do?

A. Show the order in which steps run

B. Join a box to its sub-boxes below it ✓

Lines show which sub-problems belong to which parent box. They do not show a time order.

3. A structure diagram for a school library system has the top box 'Library system'. Which is a sensible box on the level below?

A. Issue a book ✓

B. Library system

Each lower box is one sub-problem of the whole problem, so 'Issue a book' fits. Repeating the top box adds no new part.

4. Boxes 'Enter marks' and 'Print report' are both directly under 'Marks system'. What does this tell you?

A. They are on the same level ✓

B. 'Print report' is a sub-problem of 'Enter marks'

Boxes joined to the same parent sit at the same level. Neither one is a part of the other.

5. Does a structure diagram show the order in which the steps happen?

A. Yes, boxes are read left to right as a sequence

B. No, it shows the parts of the problem ✓

A structure diagram shows the parts only. A flowchart or pseudocode shows the order of the steps.

Match the Pairs

Top box: Library System → The top box of a structure diagram names the whole problem that is being broken down.

Library System → Borrow Book, Return Book → Lines join a box to its sub-boxes. Borrow Book and Return Book sit on the same level, below the whole problem.

Boxes at the same level are sub-problems of equal rank, each joined by a line to the same parent box → Quiz Game → Ask Question, Check Answer, Show Score

A structure diagram shows the parts of a problem, not the order in which the steps happen → Level 1: Input Marks | Calculate Grade | Print Report (left to right does not mean first to last)

Level 1: Quiz Game. Level 2: Ask Question, Check Answer. Top box: Ask Question → The top box must name the whole problem, Quiz Game, not one of the sub-problems such as Ask Question.

Start → Input Marks → Calculate Grade → Print Report → End (drawn as a structure diagram) → This shows a sequence of steps with arrows, which is a flowchart. A structure diagram shows the parts in levels joined by lines, not the order of the steps.

Key Term

structure diagram

A diagram with the whole problem in a top box, joined by lines to lower boxes for each sub-problem, in levels. It shows the parts of the problem, not the order of the steps.

Fill in the Blanks

1. Level 1: Quiz Game Level 2: Ask Questions, Mark Answers

Hint: Type the level number of the top box that holds the whole problem

2. The top box names the whole problem

Hint: Type the word for how much of the problem the top box names

3. Lines join a box to its sub-boxes

Hint: Type the word for what joins a box to the boxes below it

4. A structure diagram shows the parts , not the order

Hint: Type what a structure diagram shows instead of the order of steps

5. Ask Questions and Mark Answers: same level

Hint: Type the word that describes boxes sitting at one level together

Spot the Error

Question 1

A L0: Check stock

B L1: Record sales

C L1: Check stock

D L1: Print receipts

Line A — The top box must name the whole problem, not just one part of it. Line 1 should be 'L0: Run a school shop'. 'Check stock' is a sub-problem and belongs at level 1.

Question 2

A L0: Make a weather app

B L1: Get the data

C L2: Work out averages

D L1: Show the forecast

Line C — 'Work out averages' is a sub-problem of the whole app, so it sits at the same level as the other boxes under the top box. It should be 'L1: Work out averages', not level 2.

Question 3

A L0: Plan a party

B L1: Step 1 - Choose the food

C L1: Send invitations

Line B — A structure diagram shows the parts of the problem, not the order of the steps. Box names should not have step numbers. It should be 'L1: Choose the food'.

Question 4

A L0: Library system

B L1: Manage books

C L3: Add a new book

D L2: Remove a book

E L1: Manage members

Line C — 'Add a new book' is a sub-box of 'Manage books' (level 1), so it is level 2. Levels cannot be skipped. A line joins a box to the level directly below it.

Question 5

A L0: Cafe ordering system

B L1: IF drink THEN take order

C L1: Work out the bill

D L1: Take payment

Line B — Boxes in a structure diagram only name sub-problems. Decisions such as IF ... THEN belong in a flowchart or pseudocode. It should be 'L1: Take the order'.

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