Data flow diagrams
IPT 2010
data flow diagrams
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A data flow diagram provides more detail at a
lower then a context diagram. Data flow
diagrams represent the information system as a
number of processes that together form the
single process of a context diagram.
DFD’s focus on the flow of data between
information processes in a system.
Data flow diagrams
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They show where data is collected, organised,
analysed, stored, processed, transmitted and
displayed.
DFD’s provide a simple technique for visualising
the movement of data and describing what
participants do, rather than what the computers
do.
4 symbols used in A DATA
FLOW DIAGRAM
Process
Proce
ss
Data Flow
External Entity
External
Entity
Data Store
Data
Store
Process
Process
Process: A circle is used to represent the
processes or actions that transform inputs
to outputs.
data flow
Data Flow: An arrow is used to represent the
flow of data between the process, external
entity and data store.
External entity
External
Entity
External Entity: A square or a rectangle
represents any person or organisation that
sends data to or receives data from the
system.
Data store
Data
Store
Data Store: An open rectangle represents the
location where data is stored. It could be a
filing cabinet, hard disk or DVD.
example
finding a book in a library
Borrower
Book Details
Search
Book
Details
Call Number
Call
Number
Library
Database
Borrower
Example
dOCTOR’S SYSTEM FOR INVOICING PATIENTS AFTER A
VISIT
Doctor’s record of
visit
Medicare
Patients
Prepar
e
Invoice
Calculat
e
Fee
Patient
Fee Schedule
Receive
Paymen
ts
Patient’s Records
Medicare Records
Accounts
Receivable
ACTIVITY
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The marking system from the context
diagram exercise is extended to include
a spreadsheet to store and moderate
the marks.
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Construct a data flow diagram to show
the marking system.
textbook
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Read pg. 270 and pg.271 and answer
‘Group Task- Discussion’
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Answer Question 14 on pg.273