Data Flow Diagramming
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Data Flow Diagramming
 Used to represent processes that:
 … capture, manipulate, store, & distribute data
 … between a system & its environment
 … & among system components.
It's a Process Modeling technique!
Data Flow Diagramming
Source
input
retrieval
#
Data Store
storage
Process
output
2.0
Connector
Show that data flow
continues to another
process
Sink
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Context Diagram
 An overview; represents the System Scope
Customers
Sales orders
Reject notice
Accepted
sales order file
Inventory
System
0
Order
Entry
System
Rejected
sales order report
Sales
Manager
4
Level-0 Diagram
Customers
Sales orders
Item numbers
1.0
Reject notice
Accepted
sales order file
Inventory
System
Screen
sales
orders
3.0
Prepare
rejected
sales order
report
Master item
number list
Item prices
Rejected
sales order file
Sorted rejected
sales order file
Rejected
sales order report
Master price
list
2.0
Sort
rejected
sales order
file
Sales
Manager
Level 1 Diagram (for Process 1.0)
aka: Diagram 1.0
Sales orders
Customers
1.1
Verify
item
number
Item numbers
Master item
item
Master
number list
list
number
Verified item numbers
Reject notice
1.2
Item prices
Inventory
System
Accepted
sales order
file
Verify
price
Rejected sales order file
2.0
Masterprice
price
Master
list
list
DFD Practice
Draw a Level-0 Diagram
 Notes:
− Time card ≠ Time sheet
− Treat “Employee” as external to this system.
 Employees provide the departmental secretary with their weekly timecards. The secretary
prepares a weekly time sheet that lists each employee, the total hours worked, and the
hourly rate. The timecards are filed in a Time card history file.
 The departmental supervisor signs the time sheet if everything seems to be in order. If any
figures are unacceptable, the supervisor returns the sheet to the secretary. The acceptable
sheets from the departments are sent in the company mail to the accounting department.
 The accounting clerk uses the acceptable time sheets to calculate payroll earnings and writes
the earnings on the time sheets.
 Another clerk uses the time sheets to prepare the payroll checks, which are forwarded to
the employees. After this operation, the time sheets are filed in an off-line Time sheet
history file.
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Balancing!
Context Diagram
Level 1 Diagram (Process 1.0)
Level 0 Diagram
Level 1 Diagram (Process 2.0)
Consistency!
Context Diagram
Level 0 Diagram
Watch out for inconsistent names!
DFD Rules
 Naming Conventions
Processes
− Verb phrase = verb + object
− e.g. ValidateAccount, CalculateTax
 DFDs should:
Accurately represents the system
Be Balanced
Be Consistent
Be Readable
Data Flows
− Noun/noun phrase = adj + object
− e.g. payment, verified payment
Data Stores
− Noun/noun phrase = adj + object
− e.g. Employee, HourlyEmployee
External Agent
− Noun/noun phrase = adj + object
− Customer, Regional Warehouse,
e.g. Billing System
 Rules By Type
Process
− Must have both inputs & outputs
− At least one output must be
different
Data Flow
− Has only one direction
− Cannot return directly to the process
Data must be moved via a process
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Other Concepts
 Retrieval
 Updates
Item #
Price
Inventory Item
New item
Price
Inventory Item
Inventory Item
 Insert
 Update
 Delete
 Packet
Quantity on hand
Purged item
Student
Inventory Item
Inventory Item
application
Student
Application & resume
When items travel together
resume
#
#
P1.1
P1.1
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