2.1 - Elements of Computational Thinking (2.1.1-1.2)

Question 1

Define Abstraction. (2 Definitions)

Answer 1

• Abstraction is the process of separating ideas from reality
• It is a means of hiding unnecessary details to focus on the main purpose of a problem

Question 2

Subcategories of Abstraction

Answer 2

• Data abstraction - When details about how data is being stored are hidden
• Representational Abstraction - Analysing what is relevant to a given scenario and simplifying a problem based on this information.
• Abstraction by Generalisation - Involves grouping together similarities within a problem to identify what kind of problem it is
• Procedural Abstraction - Models what a subroutine does without considering how this is done

Question 3

State two advantages of using Abstraction in Software Development.

Answer 3

• Easier for programmers to focus on the main purpose of a program; thus reducing the time needed to spend on the project
• Reduces the complexity of programming; thus reduces memory and processing requirements
• Prevents program from becoming unnecessarily large

Question 4

Where can we see Abstraction in Computer Science?

Answer 4

• Applications
• Networks
• Operating Systems
• Data Structures
• Databases

Question 5

Potential Dangers of Abstraction

Answer 5

• Potential ‘Over-Abstraction’ which can lead to details that are actually important being removed
• Too much abstraction can detract from the engagement and appeal of programs like games as they may be too simplistic
• May make some simulations not realistic enough

Question 6

General Premise of Thinking Ahead

Answer 6

• Thinking ahead about the different components of a problem and the best way to handle them; allowing developers to consider potential problems or difficulties that could arise.
• Taking these factors into account early allows developers to design strategies to make programs easy and intuitive to use.

Question 7

What is a Precondition?

Answer 7

Preconditions are requirements which must be met before a program can be executed. If the preconditions are not met, the program will fail to execute or return an invalid answer.

Question 8

Advantages of Stating Preconditions in Documentation of a function

Answer 8

• Reduces length and complexity of program
• Easier to debug and maintain

Question 9

What are the preconditions of binary search tree?

Answer 9

Data must be stored in a tree structure and ordered

Question 10

What are the preconditions of binary search?

Answer 10

Data must be in order and must be in a structure where elements can be directly accessed

Question 11

What are the preconditions of linear search?

Answer 11

Data must be in a structure that is iterable

Question 12

What are reusable Program Components and how they are used when developing large programs

Answer 12

• Commonly used functions that can be identified when a problem is split into components
• Software is modular (E.g. object/function) and these modules can be transplanted into new software or shared at run time through the use of program libraries.

Question 13

Advantages of Reusable Program Components

Answer 13

• Makes programs easier to maintain as sections can be tested independently and updates to a specific module will update all parts of a program that use it
• Will save time as code doesn’t have to constantly be re-written
• Modules of code have already been tested; code is more reliable

Question 14

What is Caching?

Answer 14

It is temporary storage of program instructions or data (that have been used recently and may be used again) in cache; allowing for quicker access for future use

Question 15

What is Prefetching?

Answer 15

Where an algorithm predicts which instructions or data are likely to be required by a program. The data likely to be needed next is fetched and stored in a cache ready to be used by the program.

Question 16

Advantages of Caching (in Web Pages)

Answer 16

• Reduces load on webserver; less requests from the server back to the web server
• Frees bandwidth as images and text do not have to be downloaded again multiple times when being loaded
• Less time is spent waiting

Question 17

Drawbacks of Caching

Answer 17

• Effectiveness is dependant on size of cache and how often cached data is used; too small would make it ineffective but too big would mean a lot of data can be stored which would increase search times
• The wrong data being cached and having to be flushed can make sequence of data in cache harder to maintain

Question 18

Advantage and Drawback of Prefetching

Answer 18

• ADV - Minimising delays waiting for data or instructions to be fetched from storage.
• DIS - Highly accurate but complicated algorithms must be used; as they can only provide a prediction of which instructions are likely to be used and there is no guarantee that this will be right