Decomposition, abstraction and subprograms

Overview

Decomposition and abstraction with worked examples from maps, games and school reports, and how subprograms save time, simplify testing and maintenance, and can be reused.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Define decomposition.

   Model answer

   Decomposition is breaking a problem down into smaller sub-problems. Each sub-problem is simple enough to understand and solve on its own.

2. 2

   Define abstraction.

   Model answer

   Abstraction is removing detail that does not matter to the problem being solved. Only the features needed for the solution are kept.

3. 3

   Why does decomposition make a large problem easier to solve?

   Model answer

   A small sub-problem is easier to understand than the whole problem at once. Each part can be solved, written and tested separately.

4. 4

   Explain how decomposition helps a team of programmers.

   Model answer

   Different sub-problems can be handed to different programmers. The team can then work on several parts at the same time.

5. 5

   A map of a railway network shows the stations and the lines between them but not the real distances. Which technique does the map use, and why?

   Model answer

   The map is an abstraction of the real network. A passenger only needs the order of stations and the connections, so the rest is left out.

6. 6

   A program models a game of noughts and crosses. Which details of a real game would abstraction remove?

   Model answer

   Abstraction would remove the pen, the paper and the players’ appearance. The model keeps only the 3 × 3 grid, the marks and whose turn it is.

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