Context level DFD :-


STEPS TO DRAW A DATA FLOW DIAGRAM:-
Use a Data Flow Diagram (DFD) to show the relationships among the business processes within an organization to:
·   External systems,
·   External organizations,
·    Customers,
·   other business processes.


· Start from the context diagram.  Identify the parent process and the external entities with their net inputs and  
  outputs.
· Place the external entities on the diagram.  Draw the boundary. 
· Identify the data flows needed to generate the net inputs and outputs to the external entities.
· Identify the business processes to perform the work needed to generate the input and output data flows.
· Connect the data flows from the external entities to the processes.
· Identify the data stores.
· Connect the processes and data stores with data flows.
· Apply the Process Model Paradigm to verify that the diagram addresses the processing needs of all external entities.
· Apply the External Control Paradigm to further validate that the flows to the external entities are correct.
· Continue to decompose to the nth level DFD.  Draw all DFDs at one level before moving to the next level of decomposing detail.  You should decompose horizontally first to a sufficient nth level to ensure that the processes are partitioned correctly;  then you can begin to decompose vertically