State the data flow diagramming conpects

The approach to data flow diagramming is as follows:

• Create a data flow diagram for each of major outputs of system
• Work back from outputs to the inputs to construct diagram
• Add new objects where requires to the object model as you discover need for them in data flow modelling add new attributes and operations to object model as you discover need for them in data flow modelling.

One thing you have to consider is that data flow diagram is not used as a basis for devising structure of the system.