What are the Rules for making DFD  

The below factors must be considered when making DFDs: 

1.   Keep a note of all processes and external entities. Give unique names to them.

Identify the manner in which they interact with one another.

2.   Do numbering of processes.

3.   Avoid complex DFDs (if possible). 

4.   The DFD must be internally consistent. 

5.   Each process must have minimum of one input and one output. 

Data store must contain all the data elements which flow as output and input.