Data Flow Diagrams
A popular diagram used in the understanding and designing
of ISs is called a Data Flow Diagram.
 A data flow diagram is a pictorial representation of the main
areas of processing. It basically shows a big picture of how
the system works - how data flows through the system.


More info: https://www.visual-paradigm.com/tutorials/dataflow-diagram-dfd.jsp
1
Data Flow Diagrams - Symbols

A data flow diagram consists of combinations
of four symbols:
A Process (circle) is some procedure
which changes data. eg changing an
exam mark to a grade (A,B,C..).
 A Data Store (open rectangle) is a file
which acts as a storage area for data. eg
a data store may contain information on
a student.

2
An External Entity (square) is an
external source of data for a system, or
an external destination for info
generated by the system.
eg. a student is a source of data when
enrolling in a school’s system.
 A Data Flow (labelled line with arrow)
shows the direction of data flow and
what data is moving from one process
to another (or to a data store, or an
external entity).

3
Rules for DFDs

Never include verbs on data flow lines
ie.

Goes to
bank
Only include data, information or
knowledge on data flow lines
ie.
applicants
details
4
Rules for DFDs

Processes should always have a verb (action
word)
ie. Decision made
by Manager

Start designing DFD by listing all steps
involved. Include who gives what to who
and what gets done by who.
5
Data flow diagram of
Marking IS
1
Student
exam answers
Grade
exams
2
Record
Grade
Student’s grade
Student grades file
6
Activity
Draw a DFD for the borrowing system at the school
library.
 NOTES:

– each process in a DFD will be one of the seven IPs
– you could use DFD’s to show the various IPs in your case study
assignment.
7