computational thinking

[ 2.1 ]

what is representational abstraction?

what is representational abstraction?

• removing excessive details to represent a problem using only key features

• must analyse what is relevant to a scenario and simplify a problem based on this

what is data abstraction?

• details about how data is being stored are hidden

• programmers can use data structures without knowing how they are implemented

what are layers of abstraction?

• large, complex problems are split into layers of abstraction

• each layer has a different role

• the highest layers are the closest to the user

• these are usually responsible for providing a user interface

• the lowest layers perform tasks such as interacting with machine components

what is abstraction by generalisation?

• grouping parts of a problem by common characteristics to arrive at a hierarchical relationship

• allows problems to be categorised as being ‘of a particular type’

• a common solution can be used to solve these problems

what is procedural abstraction?

• allows programmers to utilise functions without knowing how they’re implemented

• once a subroutine has been written, it can be reused as a black box

why is abstraction needed?

• reduces programming time

• reduces complexity of code (through abstraction by generalisation)

• reduces the amount of memory/computational power required

• simplifies the problem so it's easier to solve/understand

• allows programmers to focus on core aspects of the problem

how is abstraction used for programming languages?

• low-level languages interact directly with computers but are difficult to write

• high-level languages abstract the machine code by providing easy-to-use syntax similar to natural language

• this makes developing programs easier as high-level languages are easier to learn and use than machine code

how is abstraction used in the TCP/IP stack?

• the TCP/IP model is an abstraction for how networks function

• each layer deals with a different part of the communication process

• each layer does not need to know how other layers function

name 4 things to consider when devising an abstract model.

• what is the problem that needs to be solved by the model?

• how will the model by used?

• who will use the model?

• which parts of the problem are relevant based on the target audience and purpose of the model?

why is it important that programmers identify the inputs and outputs of a problem?

• all computational problems consist of inputs which are processed to produce an output

• it is important to understand what information will be needed in the program

  • consider the data structures and data types involved

  • consider the input and output devices

• by thinking ahead, developers can build programs that are easy and intuitive to use

what are preconditions?

requirements for inputs which must be met before a program can be executed

why are preconditions for inputs used?

• specifying preconditions means a subroutine expects the arguments passed to it to be valid

• these can be either…

  • tested for within the code (validating inputs)

  • included in the documentation accompanying the program

• including preconditions within documentation reduces the length and complexity of the program

what is caching?

the process of storing instructions or data in cache memory after they have been used, as they may be used again

what are the benefits of caching?

• frequently-accessed content can be quickly loaded, this frees up bandwidth for other tasks on a network

• prefetching algorithms can predict which instructions are likely to soon be fetched,and load them into cache

• less time is spent waiting for instructions to be fetched

what are the drawbacks of caching?

• limited by accuracy of algorithms used

• larger caches take a long time to search

• smaller cache sizes limit how much data can be stored

what are reusable program components and why are they used?

• reusable components include:

  • classes

  • abstract data structures (e.g. queues and stacks)

  • subroutines

• commonly used functions are often packaged into libraries for reuse

• teams might create a library of components so they can be reused throughout a project

• problem decomposition is used to identify where previously-developed program components can be reused

what are the benefits of using reusable program components?

• more reliable than newly-coded components as they have already been tested

• saves time, money and resources

what are the drawbacks of using reusable program components?

• components may need to be modified to be compatible with existing software

• this can be more costly and time-consuming than developing them from scratch

what is problem decomposition?

• problem decomposition breaks a large, complex problem down into smaller sub-problems which can be solved more easily

• this makes projects easier to manage and they can be divided between programmers

what is top-down design?

• problems are broken down into sub-problems until each sub-problem is a single, self-contained task

• each sub-problem can then be solved using a single subroutine

• commonly used to divide a problem between a team

• subroutines can be developed and tested separately

why is the order in which subroutines are executed significant?

• programs may require certain inputs to be entered in a particular order by the user before processing can occur

• validating inputs must occur before the input data is used

• in some cases, it may be possible for several subroutines to be executed simultaneously

what is concurrent thinking?

• the process of completing more than one task at a given time

• this does not always mean you have to be working on multiple tasks at once

• involves giving ‘slices’ of your time to different tasks.

• parts of a problem which are related can often be solved concurrently

what is 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

what are the 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

what are the drawbacks of concurrent processing?

• there is an overhead in coordinating and switching between processes which reduces program throughput

• not all tasks are suited to being broken up and performed concurrently