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Computational thinking: abstraction, decomposition, algorithmic thinking

Answer on paper first, then reveal the mark scheme one mark at a time.

1Grade 1–32 marks

Define the following computational thinking terms.

(a) Abstraction [1]

(b) Decomposition [1]

(a) Removing / hiding unnecessary detail (to focus on what is important to solve the problem). Accept: simplifying a problem by ignoring irrelevant detail.(1)
(b) Breaking a (complex) problem down into smaller (more manageable) sub-problems / parts. Do not accept 'breaking code into lines'.(1)
Answer: (a) Removing unnecessary detail; (b) breaking a problem into smaller sub-problems.
Examiner tip: Students who just write 'making it simpler' for abstraction don't get the mark. You have to say that unnecessary detail is removed.

2Grade 4–54 marks

A map app shows a simplified map of a bus network. The map is an example of abstraction.

(a) Give two details from the real world that have been removed from the map. [2]

(b) Give one detail that has been kept, and explain why it is needed. [2]

(a) One removed detail, e.g. exact distances / scale; buildings; roads not on bus routes; terrain / hills; traffic; street furniture; exact road shapes / bends. Do not accept vague answers such as 'unnecessary details', or a detail the map still needs (e.g. stop names).(1)
(a) A second, different removed detail (not a repeat of the first in other words).(1)
(b) A relevant kept detail, e.g. the order of stops / stop names; route numbers or names; where routes connect.(1)
(b) A reason linked to that detail, e.g. so a passenger knows where to get off / so the correct bus can be chosen / so changes between routes can be planned. The reason must fit the detail given; do not accept a generic reason such as 'because it is important'.(1)
Answer: e.g. removed: exact distances, buildings; kept: order of stops so passengers know where to get off.
Examiner tip: In (b) the second mark is for saying why the user needs the detail you kept. Naming it alone only gets one mark.

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