2.1.2 Thinking Ahead

Question 1

What is the purpose of thinking ahead?

Answer 1

• Allows developers to consider problems/difficulties that may arise when software is used
• Makes programs easy and intuitive to use

Question 1

What are inputs?

Answer 1

• Any data that is required to solve a problem, often entered into a system by a user
• What the system needs to process

Question 2

What are outputs?

Answer 2

• The results that are passed back once the inputs have been processed and the problem solved
• What the system should produce

Question 3

Give examples of inputs

Answer 3

• Keyboard
• Mouse
• Microphone

Question 4

Give examples of outputs

Answer 4

• Speaker
• Printer
• Monitor

Question 5

What considerations do programmers need to make about inputs and outputs when thinking ahead?

Answer 5

• Data structure used
• Data types used
• Order of data

Question 6

What are pre-conditions?

Answer 6

• Conditions that already exist which may affect how you devise a solution to a problem
• Requirements which must be met before a program can be executed

Question 7

Where can preconditions be defined?

Answer 7

• Within the code or within documentation

Question 8

State three advantages of including preconditions within the documentation accompanying a sub-routine

Answer 8

• Reduces the length and complexity of the program
• Saves time to debug and maintain a longer program
• Makes subroutines more reusable

Question 9

What is caching?

Answer 9

• The process of storing instructions or values into cache memory after they have been used as they may need to be used again
• Instructions/programs retrieved from secondary storage and placed into RAM remain there in case they are needed again before the program using them ends

Question 10

How is caching used in storing web pages?

Answer 10

• The web pages a user frequently accesses will be cached so the next time it is accessed, content can be loaded without delay
• Reduces the requests from the client to the web server and vice versa

Question 11

What are the advantages of caching web pages?

Answer 11

• Content can be loaded without delay
• Images and texts do not have be downloaded multiple times
• Frees bandwidth for other tasks on a network
• Less time is spent waiting

Question 12

What is prefetching?

Answer 12

• Involves data being requested from RAM by the processor before it is actually required

Question 13

Give limitations of caching

Answer 13

• Accuracy of algorithms used in prefetching/wrong data is often fetched and cached which then has to be removed
• Maintaining correct sequence of data is problematic
• Predictive logic - caching algorithms are complicated to implement

Question 14

State some advantages of using reusable program components

Answer 14

• Shortens development time
• Saves systems resources
• Lowers development costs
• Reduces redundant code

Question 15

State disadvantages of using reusable program components

Answer 15

• May be compatibility issues with the rest of the software
• Components may need to be modified, sometime more costly and time-consuming than developing in house

Question 16

What is an advantage of caching?

Answer 16

• Faster retrieval times as fetched data from secondary storage is much slower than fetching from RAM

Question 17

What are the advantages of pre-written routines

Answer 17

• Compiled, tested and error free
• Use of libraries saves development time
• May have been written indifferent source language
• Programmers can take advantage of other programmers’ expertise