Thinking Ahead Flashcards
1
Q
What is the Advantage of Thinking Ahead
A
- Allows developers to consider problems that may arise later
- Taking these factors into account at an early stage, developers can design strategies to make programs easy and intuitive to use
2
Q
What are the Elements of Thinking Ahead
A
- Inputs and Ouputs
- Preconditions
- Cashing
- Decompoistion
3
Q
Describe the Inputs and Ouputs of Thinking Ahead
A
- Inputs include any data that is required to solve a problem and the method of input
- Outputs are the results that are passed back once the inputs have been processed and the problem solved
- Designers must decide on a suitable data type, structure and method to use in order to present the solution
4
Q
Why is good to specificy preconditions
A
Specifying preconditions means that a subroutine can expect the parameters to meet certain criteria
5
Q
What are Preconditions
A
Requirements which must be met before a program can be executed
6
Q
Why is it good to specificy preconditions in the documentation accompying code
A
- Reduces the length and complexity of the program
- Saves time needed to debug and maintain a longer program
- Sub-rountines can be reused without error
7
Q
Describe examples of some methods and their preconditions
A
- Linear search - data must be in a structure that can be moved through one element at a time
- Binary search - data must be in order and must be in a structure where elements can be directly accessed
- Binary search tree - data must be stored in a tree structure and ordered to allow a binary search
- Hash table - data must be stored in a hash table and the method of dealing with collisions must be understood
8
Q
How is Cashing used in Thinking Ahead
A
- Caching is the process of storing data in cache memory after it have been used
- This saves time which would have been needed to store and retrieve the data again
- When you are designing your own programs, you should pay attention to any areas where caching might be beneficial
- If you need to process all of the records in a file, it might be more effective to read the whole file into an array, and carry out subsequent processes against the array, than to repeatedly read and write to an external file
9
Q
What are the Potential Drawbacks of Caching
A
- Cache can become outdated if original is updated leading to inconsistences in the data (secuirty risk against data protection if stayed in cahce for a long time)
- Larger cache takes long time to search through
- Takes up storage space
- Only limited storage space
10
Q
What is Prefetching
A
- A more advanced variation of caching
- In which algorithms predict which instructions are likely to soon be fetched
- The instructions and data are loaded and stored in cache before they are fetched
- By thinking ahead, therefore, less time is spent waiting for instructions to be loaded into RAM from the hard disk
11
Q
What are the Limitations of Prefetching
A
- The accuracy of the algorithms used in prefetching is a limitation, as they can only provide an informed prediction as to the instructions which are likely to be used and there is no guarantee that this will be right
- The effectiveness of caching depends on how well a caching algorithm is able to manage the cache, larger caches still take a long time to search and so cache size limits how much data can be stored
12
Q
How is Decomposition used in Thinking Ahead
A
- By breaking the task into smaller simplier tasks
- It allows programers to identify where program components developed in the past, or externally-sourced program components, can be reused to simplify the development process
- Common reused used functions are libraries
13
Q
What are the Advantages of using Reusable Components
A
- Better tested so more reliable
- Saves time creating code
- Saves development costs.
- However, it may not always be possible since components may not be compatible
