DFD for an Online Library System

Elements

• External entities: Member, Librarian
• Processes: 1.0 Register Member, 2.0 Search Book, 3.0 Issue Book, 4.0 Return Book, 5.0 Calculate Fine
• Data stores: D1 Member File, D2 Book Catalogue, D3 Issue/Return Record, D4 Fine Record

Level 0: Context diagram

                registration details, search request,
                issue / return request, fine payment
   [ Member ] ------------------------------------> (  0  Online  )
   [ Member ] <------------------------------------ (  Library    )
                login status, search results,         (  System     )
                issue slip, fine receipt                  ^   |
                                                          |   v
   [ Librarian ] -- book details, member approval --------+   |
   [ Librarian ] <-------- reports, overdue list -------------+

Level 1 DFD

[Member]--registration details-->(1.0 Register Member)--member record-->[D1 Member File]
[Member]--search request-->(2.0 Search Book)<--book data--[D2 Book Catalogue]
(2.0 Search Book)--search results-->[Member]
[Member]--issue request-->(3.0 Issue Book)
(3.0 Issue Book)<--member check--[D1 Member File]
(3.0 Issue Book)<--availability / update copies-->[D2 Book Catalogue]
(3.0 Issue Book)--issue entry-->[D3 Issue/Return Record]
(3.0 Issue Book)--issue slip-->[Member]
[Member]--return request-->(4.0 Return Book)
(4.0 Return Book)<--issue entry-->[D3 Issue/Return Record]
(4.0 Return Book)--update copies-->[D2 Book Catalogue]
(4.0 Return Book)--return date-->(5.0 Calculate Fine)
(5.0 Calculate Fine)--fine record-->[D4 Fine Record]
(5.0 Calculate Fine)--fine receipt-->[Member]
[Librarian]--book details-->[D2 Book Catalogue]
[Librarian]<--overdue / fine reports--[D3, D4]

Data flow summary

Process	Inputs	Outputs
1.0 Register Member	Registration details	Member record to D1, confirmation
2.0 Search Book	Search request, D2 data	Search results
3.0 Issue Book	Issue request, D1, D2	Issue entry to D3, updated D2, issue slip
4.0 Return Book	Return request, D3	Updated D3 and D2, return date
5.0 Calculate Fine	Return date, due date	Fine to D4, fine receipt

Rules followed

• Every process has at least one input and one output.
• Data stores connect only to processes, never directly to entities.
• Data flows are labelled; the Level 1 inputs and outputs match the context diagram (balancing).

In the exam, draw the diagram with circles (processes), rectangles (entities), open rectangles (data stores) and labelled arrows.