Data Flow Diagram (DFD) depicts the flow of information and the transformation applied when a data moves in and out from a system. The overall system is represented and described using input, processing and output in the DFD. The inputs can be:
- Book request when a student requests for a book.
- Library card when the student has to show or submit his/her identity as a proof.
The overall processing unit will contain the following output that a system will produce or generate:
- Book will be the output as the book demanded by the student will be given to them.
- Information of demanded book should be displayed by the library information system that can be used by the student while selecting the book which makes it easier for the student.
- Level 0 DFD –

- Level 1 DFD –
At this level, the system has to show or exposed with more details of processing.
The processes that are important to be carried out are:
- Book delivery
- Search by topic
List of authors, List of Titles, List of Topics, the bookshelves from which books can be located are some information that is required for these processes. Data store is used to represent this type of information.

- Level 2 DFD –

Out of scope:
Other activities like purchasing of new books, replacement of old books or charging a fine are not considered in the above system.
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