DFD
examples
1
Example 1
Students send in an application form containing
their personal details, and their desired
course. The university checks that the course
is available and that the student has
necessary academic qualifications.
If the course is available the student is enrolled
in the course, and the university confirms the
enrolment by sending a confirmation letter to
the student.
If the course is unavailable the student is sent a
rejection letter.
2
.
1. Read the problem description carefully
looking for:
 people/organisations/things that supply
information to or use information from the
system => external entities (EE)
actions/doing words/verbs => Processes (P)
movement/exchange of information/data
between external entities to processes, and
processes to processes => data flows (DF)
store/record information/data => data
stores(DS)
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2. Walk through the system in its logical sequence.
A student (EE) sends in an application form (DF)
containing their personal details, and their desired
course
The university checks (P) that the course is
available.
If the course is available the student is enrolled (P)
in the course, and the university confirms (P) the
enrolment by sending a confirmation letter (DF) that
they are registered for the course to the student.
Or if the course is unavailable the student is sent a
rejection letter (DF).
4
Context diagram
 Highest level DFD.
 Has data flows, external entities, one process
(system in focus) and no data stores.
 Shows the system boundary and interactions with
external entities.
In this case:
External entity
Process
Data Flows
- Student
- Student Administration
process application
- Application Form,
- Confirmation/Rejection Letter
5
Context diagram
Student
Application Details
Student
Administration
System
Confirmation/Rejection Details
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System/Level 0 DFD
External entity
Processes
Data Flows
Data Stores
- Student
- Check available
- Enrol student
- Confirm Registration
- Application Form
- Course Details
- Course Enrolment Details
- Student Details
- Confirmation/Rejection Letter
- Courses
- Students
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System/Level 0 DFD
Confirmation/Rejection Details
Student
Application
Details
1.0
Check
Course
Available
Course Details
Accepted/
Rejected
Selections
2.0
Enrol
Student
Courses
Course Details
Course Enrolment Details
Students
Registration
Details
Student Details
3.0
Confirm
Registered
8
Example 2
Hoosier Burger's food ordering system
The restaurant uses an information system
that takes customer orders, sends the order
to the kitchen, monitors the goods sold and
inventory, and generates reports for
management
9
Hoosier Burger's food ordering
system
The restaurant uses an information system
that takes customer orders, sends the order
to the kitchen, monitors the goods sold and
inventory, and generates reports for
management
10
Context Diagram
Context diagram
shows the
system
boundaries,
external entities
that interact with
the system, and
major
information flows
between entities
and the system.
NOTE: only one process symbol, and no
data stores shown.
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Level-0 DFD
Level-0 DFD
shows the
system’s major
processes, data
flows, and data
stores at a high
level of
abstraction.
Processes are labeled 1.0, 2.0, etc. These will be decomposed into
more primitive (lower-level) DFDs.
12
Example 3
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 •
Context Diagram of Order System
Order
CUSTOMER
In-Stock
Request
Payment
Status
Message
Invoice
0
Order
System
Inventory
Reports
ACCOUNTING
WAREHOUSE
Shipping
Order
Shipping Confirmation
Level-0 of Order System
Order
In-Stock Request
CUSTOMER
WAREHOUSE
1.0
Status
Message
Status Data
Order
Data
2.0
Shipping
Confirmation
Shipping
Order
Check
Status
D1
Issue
Status
Messages
3.0
Pending
Orders
Generate
Shipping
Order
Order Data
Payment
4.0
Order Data
Invoice
Manage
Accounts
Receivable
5.0
Accounting Data
D2
Accounts Receivable Data
Produce
Reports
Accounts
Receivable
Inventory
Reports
ACCOUNTING
Example 4
• Perfect Pizza wants to install a system to record orders
for pizza and chicken wings. When regular customers
call Perfect Pizza on the phone, their phone number
goes automatically into the Pizza system. The phone
number invokes the name, address, and last order date
comes automatically up on the screen. Once the order is
taken, the total, including tax and delivery, is calculated.
Then the order is given to the cook. A receipt is printed.
Occasionally, special offer (coupons) is printed so the
customer can get a discount. Drivers who make
deliveries give customers a copy of the receipt and
coupon (if any). Weekly totals are kept for comparison
with last year’s performance.
• Draw a context diagram for Perfect Pizza
• Explode the context-level diagram showing all the major
processes.
Perfect Pizza: Context Level Diagram
Weekly
Report
Phone Number
Customer
Customer Order
Customer Info
Delivery
Person
Delivery
Information
Management
0
Customer
Order
System
Cook Order
Cook
Perfect
Pizza:
Current
Logical
Level
0
Diagram
Customer Order
Customer
Phone
Number
1.0
Find
Customer
Record
Customer
Info
Customer
Information
Customer
Record
2.0
Take
Customer
Order
Order
Information
Customer
History
Order
Information
D2 Customer History
D1 Customer Master
Customer
Record
3.0
Print
Delivery
Order
D3
Sales Records
Sales Info
5.0
Add
Customer
Record
Weekly Report
Management
7.0
Print
Weekly
Totals
Delivery
Information
Delivery
Person
Discount
Info
6.0
Send
Order
to Cook
Cook
Order
Cook
Customer Customer
Order
Perfect Pizza: Current Logical Child Diagram
Customer
History
Order
Information
3.1
Determine
Customer
Discount
D2 Customer History
Customer
Information
3.2
Record
Discount
Discount
Amount
3.3
Print
Delivery
Instructions
Delivery
Information
Discount
Information
D3
Sales Records
Perfect Pizza: Current Logical Child Diagram
Customer Information
5.1
Record
Customer
Information
Raw
Customer
Information
5.2
Store
Customer
Record
Customer
Record
D1 Customer Master