1. Data Flow Diagramming

2. Data Flow Diagramming Used to represent processes that:
… capture, manipulate, store, & distribute data
… between a system & its environment
… & among system components.

3. Data Flow Diagramming Source input retrieval storage output Sink
Data Store #
Process
storage
output
Sink
2.0
Connector
Show that data flow
continues to another
process

4. Context Diagram
An overview - shows the relationship between the external agents and the system
Customers
Sales orders
Reject notice
Order
Entry
System
Accepted
sales order file
Rejected
sales order report
Inventory
System
Sales
Manager

5. Level-0 Diagram
Shows the decomposition of the main system in to its major processes & the data that flows between them.
Do not include all data stores here. Only the ones shared between the major processes.
Will get too busy!
Customers
Sales orders
1.0
Screen
sales
orders
Reject notice
Accepted
sales order file
Rejected sales order file
2.0
Sort
rejected
sales order
file
Inventory
System
Sorted rejected sales order file
3.0
Prepare
rejected
sales order
report
Rejected sales order report
Sales
Manager

6. Level 1 Diagram (for Process 1.0) aka: Diagram 1.0
Customers
Sales orders
1.1
Verify
item
number
Master item
number list
Master item
number list
Item numbers
Verified item numbers
1.2
Verify
price
Reject notice
Master price list
Item prices
Master price
list
Accepted
sales order
file
Inventory
System
Rejected sales order file
2.0

7. 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.

8. Balancing! Level 1 Diagram (Process 1.0) Context Diagram
Level 0 Diagram
Level 1 Diagram (Process 2.0)

9. Consistency! Context Diagram Level 0 Diagram
Watch out for inconsistent names!

10. DFD Rules Naming Conventions Rules By Type DFDs should: Processes
Accurately represent the system
Be Balanced
Be Consistent
Be Readable
Naming Conventions
Processes
Verb phrase = verb + object
e.g. ValidateAccount, CalculateTax
Data Flows
Noun/noun phrase = adj + object
e.g. payment, verified payment
Data Stores
e.g. Employee, HourlyEmployee
External Agent
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

11. Other Concepts Retrieval Updates Packet Insert Update Delete
Price
Inventory Item
Item #
Price
Inventory Item
New item
Inventory Item
Quantity on hand
Inventory Item
Purged item
Inventory Item
Student
Application & resume
Student
application
When items travel together
resume #
P1.1 #
P1.1