The document defines and explains data flow diagrams (DFDs). DFDs show the flow of data through a system using common symbols like processes, data stores, external entities, and data flows. Processes represent actions performed on the data, data stores hold the data, external entities interact with the system, and data flows show movement of data. The document provides examples of how to construct DFDs and properly use the symbols to model a system at different levels of abstraction from context to lower level diagrams.

1. Data Flow Diagram

2. Definition
• In the late 1970s data-flow diagrams (DFDs)
were introduced and popularized for
structured analysis and design (Gane and
Sarson 1979).
• DFDs show the flow of data from external
entities into the system, showed how the data
moved from one process to another, as well as
its logical storage.

3. Data Flow Diagram
• Data flow diagram (DFD) is a picture of the
movement of data between external entities
and the processes and data stores within a
system

4. Symbols and meaning
• Squares representing external entities, which are
sources or destinations of data.
• Rounded rectangles representing processes, which
take data as input, do something to it, and output it.
• Arrows representing the data flows, which can either
be electronic data or physical items.
• Open-ended rectangles representing data stores,
including electronic stores such as databases or XML
files and physical stores such as or filing cabinets or
stacks of paper.

5. DFD Symbols (Gane & Sarson)
Process
DataFlow
DataStore
Source/Sink (External Entity)

6. Example of DFD
1.0
Check
Status
2.0
Issue
Status
Messages
3.0
Generate
Shipping
Order
ACCOUNTING
CUSTOMER WAREHOUSE
4.0
Manage
Accounts
Receivable
5.0
Produce
Reports
Order In-Stock Request
Status Data
Status
Message
Pending
Orders
D1
Order
Data
Order Data
Shipping
Order
Shipping
Confirmation
Invoice
Payment
Accounts
Receivable
D2
Accounting Data Accounts Receivable Data
Order Data
Inventory
Reports

7. Process
Grade Detail
1.0
Produce
Grade
Report
Grade Report
• Work or actions performed on data (inside the
system)
• Labels should be verb phrases
• Receives input data and produces output

8. Rule 1: Process
• Can have more than one outgoing data flow or
more than one incoming data flow
1.0
Grade
Student
Work
Submitted Work
Student Grade
Graded Work
3.0
Calculated
Gross
Pay
Pay Rate
Hours Worked
Gross Pay

9. Rule 2: Process
Order Accepted Order
2.0
Assemble
Order
Inventory
Change
1.0
Verify
Order

10. Process: Correct/Incorrect?
Services Perfomed
5.0
Create
Invoice
Invoice
Apply
Insurance
Premium
Policy Number Payment Amount
Hours Worked
2.1
Calculate
Gross
Pay
Pay Rate

11. Data Flow
• Is a path for data to move from one part of the IS
to another
• Arrows depicting movement of data
• Can represent flow between process and data
store by two separate arrows
2.1
Post
Payment
Payment Detail
Invoice Detail Accounts
Receivable
D1

12. Data Flow: Correct/Incorrect?
Courses
Class
List
Students
5.0
Post
Payment
Customer
Payment
D2 Daily Payments
Daily
Payment
6.0
Prepare
Deposit

13. Data Store
Students
D1
• Is used in a DFD to represent data that the
system stores
• Labels should be noun phrases

14. Rule: Data Store
• Must have at least one incoming and one
outgoing data flow
Customer Payment
Daily
Payments
D1
Daily Payment

15. Data Store: Correct/Incorrect?
2.0
Book
Flight
Fight
Request
Passengers
D2 Accounts
Receivable
Invoice
Detail
Payment
Detail
3.0
Post
Payment

16. Source/Sink (External Entity)
CUSTOMER Invoice
Order 1.0
Verify
Order
• External entity that is origin or destination of
data (outside the system)
• Is the singular form of a department, outside
organisation, other IS, or person
• Labels should be noun phrases

17. Rule: Source/Sink
• Must be connected to a process by a data flow
BANK
Bank
Deposit
2.0
Prepare
Deposit

18. Source/Sink: Correct/Incorrect?
PAYROLL
DEPARTMENT
Paycheck
EMPLOYEE
CUSTOMER
Payment
3.0
Apply
Payment
CUSTOMER
Payment
Accounts
Receivable

19. Rules for Using DFD Symbols
• Data Flow That Connects
A process to another process
A process to an external entity
A process to a data store
An external entity to another external entity
An external entity to a data store
A data store to another data store
Yes No

20. List the errors of this DFD
E1
E1
P2
P1
1.0
2.0
DS1
DF2
DF2
DF6
DF4
DF3
DF1
DF5

21. Context Diagram
• Top-level view of IS
• Shows the system boundaries, external entities that
interact with the system, and major information flows
between entities and the system.
• Example: Order system that a company uses to enter
orders and apply payments against a customer’s balance

22. Context Diagram of Order System
0
Order
System
SALES
REP
CUSTOMER
WAREHOUSE
BANK
ACCOUNTING
Order
Order
Reject
Notice
Picking
List
Completed
Order
Payment Invoice
Commission Bank
Deposit
Cash
Receipts
Entry

23. Level-0 DFD
• Shows the system’s major processes, data flows, and data
stores at a high level of abstraction
• When the Context Diagram is expanded into DFD level-0,
all the connections that flow into and out of process 0
needs to be retained.

24. 1.0
Fill
Order
2.0
Create
Invoice
3.0
Apply
Payment
SALES
REP
BANK ACCOUNTING
CUSTOMER WAREHOUSE
Order
Order
Reject
Notice
Picking List
Accounts
Receivable
D1
Invoice
Invoice
Invoice
Detail
Payment
Detail
Payment
Commission Bank Deposit Cash Receipts Entry
Completed
Order

25. Lower-Level Diagrams
• Functional Decomposition
– An iterative process of breaking a system description down
into finer and finer detail
– Uses a series of increasingly detailed DFDs to describe an
IS
• Balancing
– The conservation of inputs and outputs to a data flow
process when that process is decomposed to a lower level
– Ensures that the input and output data flows of the parent
DFD are maintained on the child DFD

26. Strategies for Developing DFDs
• Top-down strategy
– Create the high-level diagrams (Context Diagram),
then low-level diagrams (Level-0 diagram), and so
on
• Bottom-up strategy
– Create the low-level diagrams, then higher-level
diagrams

27. Exercise:
M/S Precision Tools sells a line of high-quality
woodworking tools. When customers place orders
on the company’s Web site, the system checks to
see if the items are in stock, issues a status message
to the customer, and generates a shipping order to
the warehouse, which fills the order. When the
order is shipped, the customer is billed. The system
also produces various reports.
• Draw a context diagram for the order system
• Draw DFD diagram 0 for the order system

28. Identify Entities,Process,Data Stores & Data Flow
• Entities
– Customer
– Warehouse
– Accounting
• Processes
– 1.0 Check Status
– 2.0 Issue Status Messages
– 3.0 Generate Shipping Order
– 4.0 Manage Accounts Receivable
– 5.0 Produce Reports
• Data Stores
– D1 Pending Orders
– D2 Accounts Receivable
 Data Flows
 Order
 In-Stock Request
 Order Data
 Status Data
 Status Message
 Shipping Order
 Order Data
 Invoice
 Shipping Confirmation
 Payment
 Accounting Data
 Accounts Receivable Data
 Order Data
 Inventory Reports

29. Context Diagram of Order System
ACCOUNTING
WAREHOUSE
CUSTOMER
0
Order
System
Order
Payment
In-Stock
Request
Status
Message
Invoice Shipping Confirmation
Shipping
Order
Inventory
Reports

30. 1.0
Check
Status
2.0
Issue
Status
Messages
3.0
Generate
Shipping
Order
ACCOUNTING
CUSTOMER WAREHOUSE
4.0
Manage
Accounts
Receivable
5.0
Produce
Reports
Order In-Stock Request
Status Data
Status
Message
Pending
Orders
D1
Order
Data
Order Data
Shipping
Order
Shipping
Confirmation
Invoice
Payment
Accounts
Receivable
D2
Accounting Data Accounts Receivable Data
Order Data
Inventory
Reports