1. Data Flow Diagramming

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

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

4. Context Diagram An overview Represents the System Scope Customers
Sales orders
Accepted
sales order file
Rejected
sales order report
Order
Entry
System
Inventory
System
Sales
Manager

5. Level-0 Diagram Customers Sales orders Item numbers Item prices
Master item
number list
1.0
Screen
sales
orders
Item prices
Master price list
Accepted
sales order file
Rejected sales order file
2.0
Sort
rejected
sales order
file
Sorted rejected sales order file
Inventory
System
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
Accepted
sales order
file
1.2
Verify
price
Inventory
System
Item prices
Master price list
Master price
list
Rejected sales order file
2.0

7. DFD Rules Naming Conventions Rules By Type DFDs should: Processes
Accurately represents 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

8. 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

9. 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.