2. 1. 2 Thinking Ahead

Question 1

Inputs and Outputs

Answer 1

• Must be able to outline what the inputs and outputs are in a given scenario
• Must be able to explain why you have chosen these
• Must be able to outline how the data is captured or relayed back to the user

Question 2

Preconditions

Answer 2

• Requirements which must be met before program can be executed, if not met the program will fail to execute or return an invalid answer
• Preconditions can be tested for within the code but are more often included in the documentation accompanying the code
• Think of preconditions as sensible restrictions that are essential to the success of the solution, can have implications on the time and cost of the solution
• In the case of prepping a meal for friends, the preconditions would be, number of friends, available time, costs, dietary requirements etc
• In an exam, in real life scenarios you need to discuss some realistic preconditions that could affect the solution

Question 3

Caching and Prefetching

Answer 3

• Process of storing instructions or values in cache memory after they have been used, may be used again
• Saves time, closer to retrieve compared to going back to secondary storage again
• Web pages usually cached, content can be loaded without any delay, images and texts don’t need to be redownloaded multiple times, frees up bandwidth for other tasks on a network
• Prefetching is a more advanced variation of caching, algorithm predict which instructions are likely to soon be fetched, loaded and stored in cache before they are fetched (actually required)
• Less time spent waiting for instructions to be loaded into RAM from the HDD
• Limitation, accuracy of algorithms used, no guarantee that instructions fetched will actually be right
• Effectiveness off caching dependent on how well caching algorithm is able to manage cache
• Larger cache still takes time to search cache size limits how much data can be stored
• This form of thinking ahead is difficult to implement but can significantly improve performance if implemented effectively

Question 4

Reusable Program Components

Answer 4

• Commonly used functions often packaged into libraries for reuse
• Teams working on large programs may also use certain components in multiple places, may put together a library so these components can be reused
• Reusable components include, implementations of abstract data structures (stacks, queues), classes and subroutines
• When designing software, problem decomposed (broken down into smaller simpler tasks), allows devs to think ahead about how each task can be solved
• Allows them to identify where program components developed in the past or externally-sourced program components (third-party) can be reused to simplify the development process
• For example, BOTW 2 used old models to reduce the overall time to develop the game (did not have to remake older models, spend time on new ones)