Data Flow Diagram

Question 1

What is an invalid connection?

Answer 1

In a Data Flow Diagram (DFD), an invalid connection refers to a data flow or relationship that should not exist in the diagram. It occurs when a data flow links two components or processes that are not logically related, or when a process has input or output data flows that do not match its function or purpose.

For example, in a DFD of a payroll system, an invalid connection could be a data flow between the Payroll process and an external component that is not involved in the payroll system, such as a marketing department. This would be incorrect because the marketing department has no logical relationship to the payroll process.

Question 2

DFD 0

Answer 2

• Has one square
• This represents the main business and who works for the business
• Circle is for external entities - human/business/task
• Arrows are processes between external & business - can only go way and can’t move diagonally
• Entities cannot talk to eachother, only through the business

Question 3

DFD 1

Answer 3

• Boxes for processes instead of arrows
• Process boxes are numbered
• No more than 7 boxes
• Arrows show how processes connect entities and can elaborate on the process
• Entities can only talk through processes
• Can repeat an entity if theres too many arrows but a line through the circle to show its the same entity
• May have data stores labelled D1 or D2 etc