Data Flow Diagram

Editor's Notes

1. Use example of borrow library book here to illustrate the different components. Student is external passes in request (book and student details) into validate student process output valid student request into reserve book process. Two data stores, students and loans. Output back to student is book; Case study - Just A Line system
2. sides of context process box = system boundary Example context diagram for library, inputs= book request, book return and output = book; external entity = student. Go through the case study - context Fig 3.4 pg 32; level 1- Fig 3.5 pg 32 level 2 - Fig 3.6 pg 33
3. Balancing - Give example of Level 1 with 3 processes, 1,2,3 and inputs between them. In level 2 add in extra flow and leave out one of the flows. Also at level 2 introduce new flows that are internal to level 2 to show that that is OK e.g. for combining dataflows - use level 1 diagram with customer inputting deposit to accept booking process and cutomer inputting balance to issue ticket process. Context diagram then has one input flow of payment = deposit +balance.