IGCSE Computer Science Paper 2 Definitions Worksheet: 7b Decomposition and Sub-systems (Modules 94–106)
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Key terms
Write what each term means, in your own words.
1
sub-system
2
hierarchy of sub-systems
3
input
4
process
5
output
6
storage
7
Input, Process, Output, Storage
8
sub-problem
9
test each sub-problem separately
10
team work and reuse
Answer Key
IGCSE Computer Science Paper 2 · Modules 94–106 · Student wording will vary for definitions
1sub-system — A smaller part of a computer system that does one job within the whole system, such as the CPU, memory or storage in a computer. It is not the whole system.
2hierarchy of sub-systems — Each sub-system can be split into smaller sub-systems, level by level, until every part does one simple job. A sub-system at one level is a system at the next.
3input — Data that goes into a system from a user, a sensor or a file, such as a typed name, a temperature reading or a line read from a stored file.
4process — An action or calculation a solution carries out on its data, such as adding a total, comparing a value with a limit, sorting or searching, or making a decision.
5output — The result a solution gives out, such as a message on screen, a printout, a sound or a signal that switches a device on or off.
6storage — Data the solution must keep, in a variable, file or database, so it can be used again later. It is not the same as input or output.
7Input, Process, Output, Storage — Read the scenario and sort every part into input (data in), process (what is done), output (result shown) or storage (data kept). Then check nothing is missing or in the wrong group.
8sub-problem — A small part of a bigger problem. It is easier to understand and solve than the whole, so splitting a problem up makes it manageable and makes mistakes easier to find.
9test each sub-problem separately — Each sub-problem is tested on its own before being joined to the rest, so an error is traced to the part that causes it and only that part needs fixing, not the whole program.
10team work and reuse — Different programmers write separate sub-problems at the same time, using their own skills, and finished parts such as a validation subroutine can be reused in other programs.