A1 · Decomposition

Spec reference: Section A - Computational Thinking
Key idea: Break a complex problem into smaller, manageable sub-problems.

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▶ Decomposition

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Identifying problems and processes

Before you can decompose a problem, you need to clearly identify and describe it. This means:

• Stating what the problem actually is.
• Identifying the inputs - what data goes in.
• Identifying the outputs - what the system should produce.
• Identifying the processes - what transformations need to happen.

Example: Online shopping checkout

Element	Description
Problem	A customer needs to buy items and pay for them online
Inputs	Items in basket, delivery address, payment details
Outputs	Order confirmation, stock update, payment receipt
Processes	Calculate total, validate payment, update database, send email

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Breaking problems into distinct steps

Once you understand the problem, you break it into distinct steps - each step is a self-contained task that can be understood and completed independently.

Example: Student grade calculator

A program needs to read student marks and output their grade. Decomposed:

1. Input student marks for each subject.
2. Calculate the average mark.
3. Compare average to grade boundaries.
4. Output the grade.
5. Repeat for each student.

Each of these steps can be further decomposed. Step 3, for example:

• If average ≥ 70 → Grade A
• If average ≥ 60 → Grade B
• If average ≥ 50 → Grade C
• Otherwise → Grade U

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Describing processes in structured steps

Once decomposed, you describe each process in structured, numbered steps - similar to writing an algorithm. The language should be clear and unambiguous so that any developer (or examiner) can follow it.

Example: Library book search system

1. User enters a search term (title or author)
2. System searches the database for matching records
3. If matches found:
   3a. Display list of matching books with availability status
4. If no matches found:
   4a. Display "No results found" message
5. User selects a book from the results
6. System displays full book details and borrowing options

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Why decomposition matters in the exam

In the BTEC Unit 1 exam, you may be given a scenario and asked to:

• Identify the inputs, processes and outputs of a system.
• Break a problem into distinct steps.
• Describe a process in structured English.

Always be specific - name the actual data being input/output, not just "data goes in" and "data comes out".

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Exam-style practice

Question: A hospital needs a system to book patient appointments. Identify the inputs, processes and outputs for this system, and break the booking process into at least five structured steps.

Model answer:

Element	Description
Inputs	Patient ID, patient name, preferred date/time, doctor ID
Outputs	Booking confirmation, updated appointment schedule, reminder notification
Processes	Check doctor availability, validate patient details, create booking record, send confirmation

Structured steps:

1. Patient enters their ID and preferred appointment date/time
2. System validates the patient ID against the database
3. System checks the selected doctor's availability for that date/time
4. If the slot is available:
   4a. Create a new appointment record
   4b. Send a confirmation to the patient
5. If the slot is not available:
   5a. Display alternative available times
   5b. Patient selects alternative or exits

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Summary

Term	Meaning
Decomposition	Breaking a problem into smaller sub-problems
Sub-problem	A smaller, self-contained part of a larger problem
Structured steps	Clear numbered instructions describing a process
Inputs	Data that goes into the system
Outputs	Results produced by the system
Processes	Operations that transform inputs into outputs

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Test Yourself

Question 1 of 5

What is the main purpose of decomposition in computational thinking?