← IGCSE Computer Science Paper 2

Abstraction (7a)

Keeping only the details needed to solve a problem and leaving out the details that do not matter, e.g. a map shows roads but not every tree.

Part of: IGCSE Computer Science 0478 — 7a Program Development Life Cycle — Module 4, QCE Digital Solutions Unit 1 — Understanding Digital Problems — Module 5, WA Computer Science ATAR Year 11 — Pseudocode and Algorithm Design — Module 8

Understanding Abstraction (7a) in IGCSE Computer Science Paper 2

What it does: The score is a relevant detail the game must track. Tiny details such as the colour of each blade of grass are left out. The stop is a useful detail for a route. Storing the bus colour would be an irrelevant detail, so abstraction leaves it out. Abstraction means keeping the useful details and ignoring the ones that do not matter. The map leaves out irrelevant details (house colours) and keeps the relevant ones (routes and stops). Ignoring unnecessary detail makes the problem easier to understand and solve. Speed affects who wins the race. The keyboard brand does not change the game's rules, so it is ignored.

Common mistakes: Comments in Cambridge pseudocode start with //, not #. It should be // Bus map: only useful data. The program also shows abstraction: a bus map stores stop names and numbers but not details like tree colour. Shoe size is an irrelevant detail for a report system, and Mark is now never declared. Abstraction keeps only what is needed, so line 3 should be DECLARE Mark : INTEGER.

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This module's key terms are also in a printable crossword (Modules 1–16) and word search (Modules 1–26).

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Learning

Duo

Which statement best describes abstraction?

Keeping only the details needed to solve the problemAdding as many details as possible to the problem

Matches

DECLARE ShoeColour : STRING // for a school timetable

↓

The shoe colour is an irrelevant detail. A timetable needs only the lessons, times and rooms, so abstraction means leaving it out.

Applying

Meanings

Term

abstraction

Meaning

Keeping only the details needed to solve a problem and leaving out the details that do not matter, e.g. a map shows roads but not every tree.

Practice

// Abstraction: keep only needed details

Testing

Gaps

// keeps only the needed details

Check Answer

Spots

1# Bus map: only useful data

2DECLARE StopName : STRING

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Quick Questions

1. Which statement best describes abstraction?

A. Adding as many details as possible to the problem

B. Keeping only the details needed to solve the problem ✓

Abstraction means keeping the useful details and ignoring the ones that do not matter.

2. A map for a bus passenger shows bus routes and stops but not the colour of each house. This is an example of:

A. Abstraction ✓

B. Validation

The map leaves out irrelevant details (house colours) and keeps the relevant ones (routes and stops).

3. A school system stores a student's name, class and attendance. Which detail is probably irrelevant?

A. The student's favourite colour ✓

B. The student's class

A favourite colour does not help the school system record attendance, so abstraction leaves it out.

4. Why do programmers use abstraction when analysing a problem?

A. To make the program take longer to write

B. To focus on the important details and make the problem simpler ✓

Ignoring unnecessary detail makes the problem easier to understand and solve.

5. In a racing game, which detail is relevant to the game's rules?

A. The speed of each car ✓

B. The brand of the player's keyboard

Speed affects who wins the race. The keyboard brand does not change the game's rules, so it is ignored.

Match the Pairs

DECLARE StudentName : STRING → A school system keeps a detail it needs, such as a name, and leaves out details like favourite colour

// Ignore the trees and houses → A programmer decides which details to leave out because they do not help solve the problem

A game keeps the score because it matters, but ignores details that do not affect play → Score ← Score + 10

A bus route program stores only the stops it needs and nothing about the bus colour → DECLARE BusStop : STRING

DECLARE ShoeColour : STRING // for a school timetable → The shoe colour is an irrelevant detail. A timetable needs only the lessons, times and rooms, so abstraction means leaving it out.

// Map program: store every tree and every leaf → This keeps far too much detail. Abstraction means keeping only useful details such as roads and landmarks and ignoring the rest.

Key Term

abstraction

Keeping only the details needed to solve a problem and leaving out the details that do not matter, e.g. a map shows roads but not every tree.

Fill in the Blanks

1. // Abstraction keeps only the needed details

Hint: Type the name of the technique that keeps useful details and leaves out the rest.

2. // Hair colour is not needed for the score DECLARE Score : INTEGER

Hint: Type the data type used for a whole-number game score.

3. // A map shows roads but not every tree OUTPUT RoadName

Hint: Type the command that displays a value to the user.

4. // A school system keeps only needed data DECLARE StudentName : STRING

Hint: Type the keyword that creates a variable to store a needed detail.

5. // Only price and quantity matter here Total ← Price * Quantity

Hint: Type the arithmetic operator that multiplies the two needed values.

Spot the Error

Question 1

A # Bus map: only useful data

B DECLARE StopName : STRING

C DECLARE StopNumber : INTEGER

D OUTPUT StopName, StopNumber

Line A — Comments in Cambridge pseudocode start with //, not #. It should be // Bus map: only useful data. The program also shows abstraction: a bus map stores stop names and numbers but not details like tree colour.

Question 2

A // Report: only needed details

B DECLARE StudentName : STRING

C DECLARE ShoeSize : INTEGER

D INPUT StudentName

E INPUT Mark

Line C — Shoe size is an irrelevant detail for a report system, and Mark is now never declared. Abstraction keeps only what is needed, so line 3 should be DECLARE Mark : INTEGER.

Question 3

A DECLARE Score : INTEGER

B DECLARE Lives : INTEGER

C Score ← 0

D Lives = 3

E // Sky colour is not tracked

Line D — Assignment in Cambridge pseudocode uses the ← arrow, not =. Line 4 should be Lives ← 3. The game tracks only Score and Lives and ignores details like sky colour.

Question 4

A DECLARE RoadName : STRING

B DECLARE Distance : DECIMAL

C INPUT RoadName

D INPUT Distance

Line B — DECIMAL is not a Cambridge data type. A distance with decimal places should be declared as REAL, so line 2 should be DECLARE Distance : REAL.

Question 5

A INPUT PlayerName

B INPUT PlayerScore

C OUTPUT PlayerName, AvatarColour

D // Leaderboard ignores avatar

Line C — The leaderboard only needs the name and score. Avatar colour is an irrelevant detail that abstraction leaves out, and it was never input. Line 3 should output PlayerName, PlayerScore.

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