Requirements - Eduqas

Abstraction is the process of separating and filtering out ideas and specific details that are not needed in order to build models that concentrate only on what is needed. When planning a project, think of abstraction as focusing on what is required - not how it is done.

Models created as a result of the process of abstraction help to simplify real-world problems so that programmers can write algorithms and programs that solve those problems more easily. Computers need clear, simple instructions to work properly. To abstract a problem:

• get rid of the unimportant parts

• focus on the key information

These make the algorithm easier to design and understand.

The London underground map is an example of abstraction in the real world. It doesn’t show the buildings, roads or trees - it just shows the station names and the tube lines that people need to be able to get around.

Detail such as timing between stations and routing is not required at this level, as it is an abstraction.

When a customer visits the cinema, the information collected might include: their name, age, seat number, drinks and snacks ordered, time of booking, the ticket design, the cinema staff who served them and their payment method.

To book a ticket the only information that might be required is:

• customer name

• age (for age restrictions)

• seat number

In this example, abstraction is used to only keep what is needed to make the system work.

Structured programming is sometimes referred to as modular programming. It involves decomposing a program into manageable chunks to perform individual tasks. The individual tasks can be written as subroutines such as functions or procedures and combined to create a main program. This is known as modularity.

Modularity turns the smaller tasks from decomposition into subroutines. These are separate blocks of code that do one specific job.

The advantages of modularity are:

• code is easier to understand

• code is easier to test

• code is easier to re-use.

This is how the decomposition of a program for users to log into a system might look:

• ask for the username and password from the user

• check if the user is in the user list

• check if the password matches

• display Access granted or Access denied.

Before a programmer writes a program, it is important to understand exactly what the program needs to do. This means understanding the problem and analysing a set of requirements. This is the first step in solving the problem to find the correct solution.

The requirements are a list of things the program must do and include:

• inputs - the data needed by the program
• processes - what the program must do with the data
• outputs - what the program should tell the user.

The requirements may also include the limitations of the program, the type of user interface and any additional rules the program needs to follow.

To create a quiz for students, firstly the designer should analyse the requirements of the quiz and identify what is needed to solve the problem (ie to create the quiz.) Then create a plan showing:

• what the program must include
• what data is required and where it comes from
• how the data will be processed
• what the output should look like
• which data structures or algorithms should be used.

• The program must display 10 multiple choice questions.
• The user must input their answer.
• The program must check if the answer is correct or not.
• The program must display the total number of correct answers.
• A list of questions and answers is needed.
• A loop is needed to repeat the questions.
• A total variable is needed to count the number of correct answers.