5.2 Data Flow Diagrams Flashcards
What are level 0 Data flow diagrams
Context diagrams - they show little detail but enable the user to gain an over view of how information flows through the system
What are level 1 data flow diagrams
They show how the main processes are broken down into sub processes.
Rules and tips for data flow diagrams
- Each process needs an input and an output
- each data store should have atleast one data flow in and one data flow out
- Data stored in a system must go through a process
- all processes must go to another process or data store
- data flows in one direction
- each data flow connects to at least one process
What is an entity
External objects outside of the system that the system communicates with.
They are sometimes sources and destinations of the systems inputs and outputs.
E.g. customer places an order via an e-commerce website ( external entity)
What is a process
Anything that changes the data and produces an output. They represent the functionalities of the system. A process can only exist once on a DFD
What is a data store
Represents stored data or control at rest. They are used when different processes need to share information but are active at different times.
What is the purpose of a rectangle as a standard DFD symbol
External entity
What is the purpose of a curved rectangle on a DFD
Process
What is the purpose of an arrow on a DFD
Data flow
What is the purpose of an open ended rectangle that’s split vertically on the left on a DFD
Data store
Impacts of affecting the flow of information in information systems DFD
Complete or partial system failure - delay in the flow of data
Human error - data being lost or processed incorrectly
Breakdown in a working relationship - delay in the flow of data, delay in processing, delay in storage
