Notes for OCR A Level Computer Science, first examined in 2016 (AS) and 2017 (A2). Notes written from course text books and other third party resources and research. Comprehensively mapped to the specification. I got an A* using them.
(02) Algorithms and Programming
2.1.1 Thinking Abstractly
(a) The nature of abstraction.
Abstraction is a “Concept of Reality” – it helps to solve a problem by representing it in a more simple
way. It can be used to test if a factor is important in a scenario for example. A Lot of information in a
problem is not important to solving it. It can be applied using many methods to interpret a variety of
problems. It is the simplification of reality into a flowing method of solution.
(b) The need for abstraction
Abstraction maximises chances of solving a problem - breaks down into the components needed,
otherwise using computers to solve problems would be impossible. Abstraction is often essential to
gain an understanding of the problem and its components. Instead of having one person plan a
large event, the task is first simplified into its basic components, such as decorations, catering and
so. Each task is solved individually and gradually more detail can be added. IT makes problems
efficient so solve in a methodical manner.
(c) The differences between an abstraction and reality.
‘Layers of Abstraction’ breaks a problem into its components, these are further broken down to
solve a particular element, different problems are solved by different components - a big system can
do a variety of tasks by using different components. Abstraction can be used to remove unnecessary
data in a model eg Craters on a solar system model or pot holes in a road. Only keep the data that is
important to complete the task at hand. This will vary on different levels.
(d) Devise an abstract model for a variety of situations.
This process can be called “Abstraction by Generalisation”, first identify the components that may
generally be used, then implement them catering for the current environment they are in. Slowly
add more detail to the model and expand on the specific details.
Abstraction is also seen when a precondition or sub-procedure is called, as we might not be aware of
how the process is completed. For example in python “print” and “input” are preconditions calling
code written by developers.
Variables are a form of Abstraction - represent a real world value. Example - A chair is an object with
a surface to sit on and legs to stand on. Each chair is an instance of the class chair.
Procedural Abstraction – Programmers use a procedure via its interface Procedure Name(a, b, c).
They receive the expected output but are not aware of how this was done, and are not concerned
with it. The procedure will have been written and tested such that it works in a versatile and robust
manner.
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Ravi Shah
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