Issuing out a book from a library
This system need to accept student information as input. Student information may contain student name, roll number, registration number and so on. The best can be roll number that is usually not repeated (although registration number is not repeated, for now I choose roll no). Advantage of preparing this DFD can be; proper knowledge of Data flow, effects of external entities in the system, determination of process in the overall system.(see also Symbols Used in DFD)
This Data Flow Diagram was taken directly from my notes so if you have any problems in understanding it, you are kindly requested to leave comment below.
In this context diagram of DFD; general symbols of DFD are used to prepare a simple model. Students, Librarian and Head of Library are the external entities. Process name is Issuing Books. The thing is, process name should be action verb that specifies the operation. Data Flow contains the data to be exchanged throughout the system from external entities to data stores through process.
Figure: Context Diagram- Issuing Books from library
Similarly, in Level 1 DFD external entities are same but processes are break down so as to clarify the operation separately.
Figure: Level 1 DFD- Issuing Books from library