Structure Diagrams (SQA National 5 Computing Science): Revision Note

Structure diagrams

What are structure diagrams?

• A structure diagram is a design technique used during the design stage of the software development process

• It shows the overall structure of a program before any code is written

• The diagram represents the main steps needed to solve a problem

• Each step can be broken down into sub-tasks, helping to plan the program in a clear and logical way

• Structure diagrams are read from top to bottom and left to right

Why use structure diagrams?

• They help visualise the program’s structure before implementation

• They make programs easier to understand, test, and maintain

• They allow programmers to identify where loops, decisions, and processes are needed

• They help to spot repetition or inefficient steps in a design before coding starts

Key components of structure diagrams

Symbol	Name	Meaning	Example
	Process	Shows an action or calculation	set totalPassengers to 0
	Selection	Shows a decision or condition	Is ticketNumber in range for today?
	Loop	Shows repetition of a process	repeat until no more passengers
	Predefined process	Refers to a separate subprogram or function	CalculateAverage()