computer science unit 2

What does designing a solution entail?

• thinking of the different components of a problem

• and how they will be handled in the best way

Why is thinking ahead important when designing a solution?

• allows developers to consider problems or difficulties

• that may arise when the software is used

what happens to inputs and what are they in this context?

• inputs are processed to produce an output

• such as data required to solve the problem ,

• which is entered into the system by the user

wha are outputs?

• results that are passed back

• once the inputs have been processed and the problem solved

What do designers typically begin by considering?

• considering what outputs are required

• based on the user’s requirements.

What is the next step after identifying the required outputs?

• identify the inputs required

• and how these need to be processed

• to achieve these outputs.

what are preconditions

• requirements which must be met

• before a program can be executed

(if not, the program will fail to execute / return an invalid answer)

what does including preconditions do?

• reduces the length and complexity of the program

• saving time needed to debug and maintain a longer program

• makes subroutines more reusable

what happens to commonly used functions?

• can be stored in libraries for reuse

• useful for teams working on large projects

whats the advantages of using reusable components?

• more reliable as tehy’ve been tested / bugs dealt with

• saves time and money

• subroutines can simply be reused in future, saves development costs

disadvantages of reusable components?

• might not always be possible

• because of compatibility issues

• so they might be modified which could be more costly than developing on your own

what is abstraction

• removing unnecessary details

• and focusing on the key features

representational abstraction?

• analysing whats relevant to a scenario

• simplifying a problem based off that

abstraction by generalisation?

• grouping together similarities within a problem,

• to identify what kind of problem it is

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

data abstraction

• when details of how

• data is being stored

• are hidden

• so programmers can make use of abstract data structures (stacks, queues, etc.,)

• without needing to know how they are implemented

procedural abstraction

• models what a subroutine does

• without considering how

• or knowing about the code used to implement it

what will complex problems make use of?

• multiple levels of abstraction

high level abstraction = ?

• closest to the user

• provide the interface to interact with the hardware

• (LESSS DETAILL)

low level of abstraction = ?

• responsible for performing the task

• though machine code

• (LOTSSS OF DETAIL)

benefits of abstraction?

• Reduces programming time

• Reduces complexity of code (through abstraction by generalisation)

• Reduces amount of memory required / computational power

• Simplifies the problem so it's easier to solve / understand (by recognising common patterns)

• Allows programmers to focus on core aspects of the problem

abstraction vs reality

• abstraction is a simplified representation of reality

• real-world entities can be represented using computational structures (tables)

• real world values can be stored a variables

thinking procedurally

• breaking down a complex problem into smaller parts

benefits of thinking procedurally

• Splits the problem into smaller chunks

• Smaller problems are more manageable

• Smaller problems are easier to solve

• To see where code can be reused in the solution

• To split tasks between different programmers

• Decomposition splits the problem into smaller sub problems

• The division can lead to the development of subroutines/modules

• The division can lead to a logical division between programmers/teams

whats a top-down design?

• also known as stepwise refinement

• a preferred method used to approach very large problems

• breaks problems into levels

whats the aim of top-down designs?

• to keep splitting problems into sub-problems until each sp can be represented as a single task

• and ideally a self-contained module or subroutine

• can then be solved by a different person

• also be tested separately

whats thinking logically

• identifying when to make a decision

• e.g. using a flowchart

what does thinking logically allow us to do?

• determine the complexity of an algorithm

• identify at which points a decision is needed

• determine the conditions of the decision

• determine the next steps depending on the outcome of the decision