← IGCSE Computer Science Paper 2

Completing and reading a structure diagram

Read the given boxes top down, then fill each gap with the sub-problem its parent box needs, so the sub-boxes together make up the parent. Ignore boxes that do not belong.

Part of: IGCSE Computer Science 0478 — 7b Decomposition and Sub-systems — Module 23

Understanding Completing and reading a structure diagram in IGCSE Computer Science Paper 2

What it does: All three sub-problems are needed to log in, so together they make up the parent box Login. The parent Calculate bill needs a tax step, so Add tax is the sub-problem that fills the gap. A sub-box must help solve the parent. Checking for a capital letter is part of checking a password. Playing music has nothing to do with it. Designing a school logo is not needed to make the quiz work, so it does not belong. 'Check answers' is a real part of a quiz game. The gap sits between asking and showing, so the missing sub-problem is the one that checks the answer.

Common mistakes: 'Buy new shoes' does not belong. Every sub-box must be part of solving the parent box. It should be a sub-problem such as 'Collect marks'. Reading top down, the parent box must be the problem that the sub-boxes together make up. Check PIN, Choose amount and Give cash make up 'ATM withdrawal', not 'Online shopping'.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

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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
A structure diagram has the top box 'Run a school canteen order system' with sub-boxes 'Take orders' and 'Print receipts', and one box is missing. Which box best fills the gap?
Draw a flowchartCalculate total cost
Matches
Weather app: Show forecast, Play music, Get data
↓
Play music is a box that does not belong. It is not needed to solve the parent problem, so remove it.
Applying
Meanings
Term
complete a structure diagram
Meaning
Read the given boxes top down, then fill each gap with the sub-problem its parent box needs, so the sub-boxes together make up the parent. Ignore boxes that do not belong.
Practice
Quiz program
Testing
Gaps
Check PIN | Enter amount |
Check Answer
Spots
1Make a school report
2 Buy new shoes

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Quick Questions

1. A structure diagram has the top box 'Run a school canteen order system' with sub-boxes 'Take orders' and 'Print receipts', and one box is missing. Which box best fills the gap?
A. Draw a flowchart
B. Calculate total cost ✓
The missing box must be a sub-problem the parent needs. Calculating the total cost fits between taking orders and printing receipts. Drawing a flowchart is a design method, not part of the canteen system.
2. Which way do you read a structure diagram to complete it?
A. Top down: start at the parent box, then work out its sub-boxes ✓
B. Bottom up: start with the smallest boxes and guess the parent
You read from the top down. The parent box is the whole problem, and each level below it splits that problem into smaller sub-problems.
3. The parent box is 'Check a password'. Its sub-boxes are 'Check length' and 'Check for a digit'. Which box would fill a third gap?
A. Play background music
B. Check for a capital letter ✓
A sub-box must help solve the parent. Checking for a capital letter is part of checking a password. Playing music has nothing to do with it.
4. True or false: the sub-boxes under a parent box should together make up the whole of the parent box.
A. True ✓
B. False
If you put the sub-problems together they should solve the parent. If a part is missing, the parent is not fully covered, so you need to fill the gap.
5. The parent box is 'Make a quiz game'. Sub-boxes are 'Ask questions', 'Check answers' and 'Design a school logo'. Which box does not belong?
A. Design a school logo ✓
B. Check answers
Designing a school logo is not needed to make the quiz work, so it does not belong. 'Check answers' is a real part of a quiz game.

Match the Pairs

Quiz game: Ask question, ___, Show score → A missing box: fill the gap with a sub-problem the parent needs, such as Check answer
Run school canteen > Take orders > Write order → Reading from the top down: start with the whole problem, then follow each level to smaller sub-problems
The sub-boxes together must make up the parent box → Login: Enter username, Enter password, Check details
Fill a missing box with a sub-problem the parent box needs → Calculate bill: Add prices, ___ = Add tax, Print receipt
Weather app: Show forecast, Play music, Get data → Play music is a box that does not belong. It is not needed to solve the parent problem, so remove it.
Login: Enter password → A sub-box is missing. Enter username and Check details are needed so the sub-boxes make up the whole parent box.

Key Term

complete a structure diagram
Read the given boxes top down, then fill each gap with the sub-problem its parent box needs, so the sub-boxes together make up the parent. Ignore boxes that do not belong.

Fill in the Blanks

1. Withdraw cash Check PIN | Enter amount | Give cash
Hint: Type the last sub-box: the step that hands the money to the customer
2. Library system Borrow book | Return book | Pay fine
Hint: Read top down and type the parent box that covers all three sub-problems
3. Find average mark Get marks | Add up marks | Divide by count
Hint: Type the missing sub-problem that finds the total, which is needed before dividing
4. Make toast Get bread | Toast bread | Wash car Box to remove: Wash car
Hint: Type the sub-box that is not part of making the parent task
5. Level 1: Online shop Level 2: Browse | Pay | Deliver Level 3: Enter card details (under Pay)
Hint: Type the level number of the boxes directly below the top box

Spot the Error

Question 1
A Make a school report
B Buy new shoes
C Calculate averages
D Print report
Line B — 'Buy new shoes' does not belong. Every sub-box must be part of solving the parent box. It should be a sub-problem such as 'Collect marks'.
Question 2
A Online shopping
B Check PIN
C Choose amount
D Give cash
Line A — Reading top down, the parent box must be the problem that the sub-boxes together make up. Check PIN, Choose amount and Give cash make up 'ATM withdrawal', not 'Online shopping'.
Question 3
A Weather station
B Record data
C Eat lunch
D Read rain gauge
Line C — 'Eat lunch' does not belong under 'Record data'. The missing box must be a sub-problem the parent needs, such as 'Read thermometer', so that the sub-boxes together make up 'Record data'.
Question 4
A Login system
B Enter details
C Check details
D Play music
Line D — 'Play music' does not belong in a login system. The missing box should be a sub-problem that the parent needs, such as 'Allow access'.
Question 5
A Mobile game
B Start game
C Play level
D Make the whole game
Line D — 'Make the whole game' just repeats the parent box. A sub-box must be a smaller part of the problem, such as 'Show high score'.

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