OCR A Level CS 2.1: Elements of Computational Thinking

Topic Flashcards

Abstraction

The process of removing unnecessary detail

Simplifying a complex problem

allows programmers to focus on only the core/necessary parts

(used in networking and higher and lower level programming languages)

Benefits of Abstraction

Allows programmer to focus on core aspects so reduces programming time/cost as faster to create the program. Factors that detract from the program can easily be ignored.

Simpler to solve the problem/ Simplifies the problem as easier to solve/understand

Program requires less memory/computational power/faster program execution

Reduces complexity of programming code so can run on lower spec computers

Completed program will be simpler for end-users to understand

Program more likely to solve the problem as unnecessary aspects will not detract from the main purpose of the program.

Why are reusable program components used in programs?

One piece of code can be used many times in multiple places, which makes code more efficient.

No need to write the same code multiple times.

Takes less time to plan/design/code the program.

Easier error detection since if you fix once, it is corrected in every place where that code is used. Less likely to have errors as code is not written multiple times.

Easier to maintain the program.

How to describe logical decisions within a program

Decision, action the program will take if true, action if fals

Global variables

Created when program starts, all subroutines can access/update its contents.

Stored in memory throughout the whole code execution. If the amount of data stored in them is large, then would make program memory intensive.

Used when variables are needed throughout the game.

Local variables

Created in the subroutine they are created in, not accessible directly from any othr subroutine

Removed from memory once subroutine ends.

Can be passed as parameters to a function to be updated, and then returned to override the original local variable.

Can be passed by reference to a subroutine to allow the content of the variable to be updated.

Concurrent processing

Processes happen at the same time/ processes overlap

One process can start before another one finishes

Each process is given a slice of processor time

Different processes can be executed in parallel by different processors/cores

Benefits of concurrent processing

More efficient processor use/ Less idle time for processor/ Greater throughput

Long running tasks do not delay short running tasks

Tasks requiring preconditions can wait and then resume execution

User is able to interact with the computer while other tasks are running

Drawbacks of concurrent processing

If lots of users are requesting for tasks to be completed, it takes longer for everyone to complete their task

Why concurrent processing is needed to allow multiple users to log in and interact with game elements at the same time

Game could have large number of requests to the server at a time, and the server needs to respond in a reasonable time. Having multiple processors handling the different requests would increase response time.

Users could override each other’s changes, so use record locking to stop edits if someone else has access to data.

Different users will have different response times, therefore the processor can still handle other requests so that performance for other users is not affected.

Why is there a need for concurrent processing

Processes are happening at the same time/ at overlapping times. One process may need to start before a second has finished. In terms of an online ticket system, individual processes are threads, each thread has a life line. One request is sent to the server, this will have a thread.

Multiple requests to the server can be made at the same time. Programming on server will need to allow multiple threads to manipulate a list of requests. Programming will need to restrict access to the database, and will allow those reading and writing to manipulate at the same time. Record locking will need implementing- more complex programming.

Will allow for multiple access to the website at the same time by different customers, and will allow for multiple ticket sales for the same event without selling the same seat twice.

Thinking Ahead

Consider inputs/outputs

Data Types

Data Structures

Order of data

Advantages of including preconditions within the documentation accompanying a subroutine

Reduces length of program

Reduces complexity of program

Saves time needed to debug and maintain a longer program

Makes subroutine more reusable

Caching

The process of temporarily storing a copy of instructions or values in cache memory after they have been used, as they may be used again. Reduces the time taken to fetch them again.

Advantages of caching webpages

Content can be loaded without delay

Images and text do not need to be downloaded multiple times

Frees bandwidth for other tasks on a network

Less time spent waiting