谁能解释这个dfd？

Question

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 !

Answer 1

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)