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I am new to Dfds . I have to make a dfd for my project so for that I am studying about them . I found this dfd on the inetrnet but I am unable to understand it's few parts , such as , why query process has been attached to the resrvation process , can we do without it ? Why cancellation table has been attaching to the railway department and why passenger is simultaneously connected to enquiry and the reservation process ? I am still unable to post any image so here is the link to the dfd http://image.slidesharecdn.com/presentation-130830092202-phpapp02/95/presentation-on-railway-reservation-system-13-638.jpg?cb=1377872947 Could anyone of you explain this dfd ? I would be very grateful to you ! Thank you !

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A data flow diagram, as the name suggests, shows the way the data traverses through a software. There is no rights or wrongs in this. It is like an algorithm. Where the arrow points to is an input to the pointed rectangle. For example, "Reservation" is an input to "Query Process" and "Query Process" outputs to "Report". It is as simple as that. This is just the way this one is designed. A report may be required, but a report can be created only if there is an input. In this case, "Query Process" creates that input, and the arrow simply shows the relation.

It is really an abstraction of the data. It cannot be designed from stratch. You need some prior diagrams :) documents to be able to create this. One of these documents is SRS(Software Requirements Specification)

  • thank you ! could you also tell me why they have attached cancellation table with the railway department and why the passenger has been simultaneously connected to the enquiry and reservation process ? Thank you ! –  Mar 22 '15 at 17:28
  • My best guess would be; if a reservation is cancelled, someone should notify railway department so that they can know the reservation is cancelled and they can resell the ticket or whatever. The other thing is, everything a passenger does in the system is probably required to fire some triggers. For example, a passenger makes a reservation, through reservation process, it is sent to railway department. Passenger can also inquiry somethings through "Inquiry" –  Mar 22 '15 at 17:32
  • Thank you and one last question , why the passenger has been simultaneously connected to the enquiry and reservation process ? –  Mar 22 '15 at 17:34
  • Updated my previous comment, could you please check this answer as accepted? :) –  Mar 22 '15 at 17:36
  • Thank you . This one is surely the last question ! I am still confused with the query processing attached with the reservation process . What query is processed and if I remove query process and it's related elements i.e, reservation , and report from my dfd , would my dfd still be correct ? Thank you ! –  Mar 22 '15 at 17:39
  • Yes, I would surely accept your answer but please answer my last question . I would be very grateful to you ! :) –  Mar 22 '15 at 17:40
  • As I mentioned there are no exact rights and wrongs in this. If you remove them, that means the system is not to generate reports related to reservations. Some other ones input and output to reservation. All those ones are contributing to reservation(as data) if you remove some parts contributing, then they wouldn't be contributing; reservation data is generated as much is included in the dfd. –  Mar 22 '15 at 18:01