2.1.1Thinking abstractly +2.1.2 Thinking ahead

Question 1

Abstraction

Answer 1

Hiding unnecessary detail and showing details that are important in context.

Question 2

Inputs

Answer 2

What the system needs to process.

Question 3

Outputs

Answer 3

What the system should produce.

Question 4

Preconditions

Answer 4

Conditions that already exist and could affect how you devise a solution to a problem.

Question 5

Subroutines, Procedures, functions and methods

Answer 5

Blocks of code that perform a task and can be reused multiple times.​

Question 6

Caching

Answer 6

Storing instructions or values in cache memory after they have been used, as they
may be used again. Results in faster retrieval times, as instructions or data don’t need to be fetched from secondary storage, which is much slower.​

Question 7

Prefetching

Answer 7

Data being requested from main memory by the processor before it is required.

Question 8

Procedural abstraction

Answer 8

The process of breaking down problems into smaller more manageable steps​

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Question 9

Data abstraction

Answer 9

a form of abstraction in which details about how data is being stored are hidden

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Question 9

Functional abstraction

Answer 9

the implementation detail of the computational method is hidden​

Question 10

Problem abstraction

Answer 10

the process of filtering out - ignoring - the characteristics of problems that are not needed in order to concentrate on those that are needed​

Question 11

The difference between abstraction and reality

Answer 11

● Abstraction is a simplified representation of reality
● Real-world values can be stored as variables and constants
● Objects in object-oriented programming are an abstraction for real-world entities
○ Attributes represent the characteristics of an object
○ Methods represent the actions a real-world object is able to perform

Question 12

2 advantages of abstraction

Answer 12

-easier for programmers to focus on the core elements
-reduces the time needed to be spent on the project
-prevents programs from getting unnecessarily large

Question 13

what is representational abstraction

Answer 13

a technique in which excessive details are removed to arrive at a representation of a problem that consists of only the key features.

Question 14

what form of abstraction involves grouping together similarities within a problem to identify what kind of problem it is

Answer 14

abstraction by generalisation

Question 15

what kind of problems make use of multiple levels of abstraction

Answer 15

large complex problems

Question 16

give two applications of layers of abstraction

Answer 16

-Networking(TCP/IP)
-programming languages

Question 17

state 2 advantages of using abstraction in programming languages

Answer 17

-easier to remember syntax in high level languages as it is closer to natural language
-coding becomes accessible to beginners

Question 18

how does object oriented programming use abstraction

Answer 18

-objects are an abstraction for real world entities.
-Attributes are an abstraction for the characteristics of an object.
-methods are an abstraction for the actions a real world object is able to perform

Question 19

what is the purpose of thinking ahead

Answer 19

to make programs easy and intuitive for users to use

Question 20

what three considerations do programmers need to make inputs and outputs when thinking ahead

Answer 20

-method of input/output
-data structures used
-data types used
-order of data

Question 21

where can pre-conditions be defined

Answer 21

within the code or within documents

Question 22

give an example where preconditions are required

Answer 22

-stack functions
check that the stack is not empty when popping an element from a stack.
check that a stack is not full when pushing an element onto a stack
-Factorial function
the number passed to the function cannot be negative

Question 23

state two advantages of including preconditions within the documentation accompanying a subroutine

Answer 23

-reduces the length of the problem
-reduces the complexity of the program
-saves time needed to debug and maintain a longer program
-makes subroutine more reusable

Question 24

how is caching used to store web pages

Answer 24

web pages that a user frequently accesses are cached, so the next time one of these pages is accessed, content can be loaded without delay

Question 25

what are the advantages of caching web pages

Answer 25

-content can be loaded without delay
-images and text don’t have to be downloaded again multiple times
-frees bandwidth for other tasks on a network
-less time is spent waiting

Question 26

give a limitation of caching

Answer 26

-accuracy of algorithm used
-effectivness of algorithm in managing the cache
-size of the cache

Question 26

Give 3 advantages of using reusable program components

Answer 26

-more reliable than new components. As they have already been tested

-as developing from scratch is not required, this saves time, money and resources

Question 26

Give two examples of reusable programs

Answer 26

-abstract data structures
-classes
-subroutines