← IGCSE Computer Science Paper 2

Writing exam answers about decomposition and abstraction

Uses key terms (sub-system, decomposition, abstraction, input, process, output, storage) correctly and gives a reason for each point, for example by using the word 'because'.

Part of: IGCSE Computer Science 0478 — 7b Decomposition and Sub-systems — Module 47

Understanding Writing exam answers about decomposition and abstraction in IGCSE Computer Science Paper 2

What it does: The sentence makes a point (easier) and gives a reason using 'because', which is what earns the mark. Each part of the system is labelled with its correct key term and matched to the scenario. Decomposition means breaking a problem into smaller parts. Removing unnecessary detail is abstraction, so mixing the two up loses marks. Inputs are the data entered into the system. Multiplying the values is the process. Storage is where data is kept for later use, such as a file or database. Showing the total on screen is an output. The definition describes decomposition, so it gets no mark for abstraction.

Common mistakes: The sentence gives no reason. A full-mark answer links the point with 'because', for example 'This helps because each part is easier to solve.'. Abstraction keeps only the key features, not all of them. The line should say 'detail and keeps key features.'.

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This module's key terms are also in a printable crossword (Modules 136–145) and word search (Modules 123–145).

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Learning
Duo
Which answer defines decomposition correctly?
Breaking a complex problem down into smaller, more manageable sub-problemsRemoving unnecessary details so only the important features remain
Matches
Abstraction is breaking a problem into smaller sub-problems.
↓
This confuses abstraction with decomposition. Breaking a problem into parts is decomposition, while abstraction is removing unnecessary detail.
Applying
Meanings
Term
full-mark answer
Meaning
Uses key terms (sub-system, decomposition, abstraction, input, process, output, storage) correctly and gives a reason for each point, for example by using the word 'because'.
Practice
Decomposition breaks a problem into smaller sub-systems.
Testing
Gaps
means breaking a problem
Check Answer
Spots
2into smaller sub-problems.
3This helps and each part

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Quick Questions

1. Which answer defines decomposition correctly?
A. Removing unnecessary details so only the important features remain
B. Breaking a complex problem down into smaller, more manageable sub-problems ✓
Decomposition means breaking a problem into smaller parts. Removing unnecessary detail is abstraction, so mixing the two up loses marks.
2. Which answer defines abstraction correctly?
A. Splitting a problem into smaller sub-systems that can be solved separately
B. Keeping only the details needed to solve the problem and ignoring the rest ✓
Abstraction is about filtering out unnecessary detail. Splitting a problem into parts is decomposition.
3. Which exam answer would earn the reason mark for 'Explain why decomposition is useful'?
A. It makes the problem easier to solve because each smaller sub-problem can be tackled separately ✓
B. Decomposition is very useful and helps a lot when writing programs
A full-mark answer links the point to a reason, often using 'because'. The vague answer gives an opinion but no reason.
4. A student writes: 'Decomposition makes testing easier because each sub-system can be tested on its own.' What is good about this answer?
A. It uses a key term and links the point to a reason ✓
B. It repeats the question without adding any reason
The word 'because' shows the reason, and 'sub-system' is a correct key term. Both help earn full marks.
5. A question asks you to list the inputs for a program that calculates the area of a rectangle. Which answer is correct?
A. The length and the width entered by the user ✓
B. Length multiplied by width to get the area
Inputs are the data entered into the system. Multiplying the values is the process.

Match the Pairs

Decomposition is breaking a problem into smaller sub-problems. → A correct one-sentence definition of decomposition that uses the key term accurately.
Abstraction is removing unnecessary detail and keeping the important parts. → A correct one-sentence definition of abstraction that uses the key term accurately.
A full-mark answer links each point to a reason, for example by using the word 'because'. → Decomposition makes the problem easier because each sub-system can be solved and tested separately.
A full-mark answer for a scenario lists the input, process, output and storage using the correct terms. → Input: score. Process: add to total. Output: display total. Storage: save to file.
Abstraction is breaking a problem into smaller sub-problems. → This confuses abstraction with decomposition. Breaking a problem into parts is decomposition, while abstraction is removing unnecessary detail.
Decomposition makes a problem easier to solve. → This gives a point but no reason. It needs a 'because' to explain why, such as because smaller parts are easier to understand and test.

Key Term

full-mark answer
Uses key terms (sub-system, decomposition, abstraction, input, process, output, storage) correctly and gives a reason for each point, for example by using the word 'because'.

Fill in the Blanks

1. Decomposition means breaking a problem down into smaller sub-problems.
Hint: Type the key term for splitting a problem into smaller parts.
2. Abstraction removes unneeded detail to focus on the important features.
Hint: Type the key term for hiding or removing unnecessary detail.
3. Decomposition makes it easier because each sub-system can be tested separately.
Hint: Type the linking word that introduces a reason in a full-mark answer.
4. The four parts are input, process, output and storage.
Hint: Type the fourth component, where data is kept for later.
5. Removing detail is abstraction, not decomposition.
Hint: Type the term that means splitting into parts, which students often confuse with abstraction.

Spot the Error

Question 1
A Decomposition splits a problem
B into smaller sub-problems.
C This helps and each part
D is easier to solve.
Line C — The sentence gives no reason. A full-mark answer links the point with 'because', for example 'This helps because each part is easier to solve.'
Question 2
A Abstraction removes unneeded
B detail and keeps all features.
C It makes a problem simpler.
Line B — Abstraction keeps only the key features, not all of them. The line should say 'detail and keeps key features.'
Question 3
A Two key terms are different.
B Decomposition = hiding detail
C Abstraction = hiding detail
Line B — This confuses decomposition with abstraction. Decomposition means splitting a problem into smaller parts, so the line should be 'Decomposition = splitting up'.
Question 4
A Scenario: a quiz app
B Input: player's answer
C Output: compare with correct
D Output: right or wrong message
E Storage: high score file
Line C — Comparing the answer with the correct one is a process, not an output. The line should start 'Process:'.
Question 5
A Scenario: library loans
B Input: book ID and member ID
C Process: check the book is in
D Process: loan receipt printed
E Storage: loan records file
Line D — A printed receipt is shown to the user, so it is an output, not a process. The line should start 'Output:'.

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