And Franchise Colleges
Data Flow Diagrams - Examples
Using SSADAM Notation
By MANSHA NAWAZ
DFD - Examples
1
Context Diagram
Order
Company
Customer
Rejected
Order
Despatch Note + Goods
DFD - Examples
2
A Complete DFD
1
Sales
Order
Check Credit
Rating
Customer
Rejected
Order
D1
Dispatch
Note
3
2
Credit
Rating
Accounts
Maintain Credit
Ratings
Warehouse
Dispatch
Goods
DFD - Examples
3
Data Flow Diagrams (DFDs) show:
The processes within the system
The datastores (files) supporting its operation
The information flows within it
The system boundary
Interactions with external entities
DFD - Examples
4
A Data Flow
Customer
An External Entity
DFD Symbols
SSADM Notation
3
Sales
A Process
Check Credit
Rating
D1
Credit
Rating
A Data Store
DFD - Examples
5
The Process Symbol
Where it’s done
Unique Number
3
Input
Data
Sales
Check Credit
Rating
Output Data
What’s done
DFD - Examples
6
The data store symbol
Writing/Updating
3
D1
Credit
Rating
Accounts
Maintain
Credit Rating
Reading
1
M = Manual data Store
D = Computer File
Sales
Check Credit
Rating
DFD - Examples
7
The Data Flow Symbol
Use Meaningful
names
Customer Balance
Self Evident Data Flows need
not be named
3
D1
Credit
Rating
Sales
Check Credit
Rating
DFD - Examples
8
Physical Resource Flow
Customer
Returned
Library Book
DFD - Examples
9
The External Entity Symbol
System Boundary
Customer
A Source
and/or sink of
data outside
the system
boundry
DFD - Examples
10
Levelling – to avoid complex DFDs, processes can be grouped into
higher level processes
2
Dispatch Goods
Process
2.1
Validated
1
Order
Dispatch
Note
2
DFD - Examples
11
A Complete DFD
1
Sales
Order
Check Credit
Rating
Customer
Rejected
Order
D1
Dispatch
Note
3
2
Credit
Rating
Accounts
Maintain Credit
Ratings
Warehouse
Dispatch
Goods
DFD - Examples
12
Repeated Symbols – to avoid crossing lines, data
stores and external entities can be repeated:
Customer
Customer
D1
Credit
Rating
A Duplicated External Entity
Duplicated Data Store
DFD - Examples
13
DFD Levels
Elementary
Functional
Level 2
Description
Get cust dets
If order>cred
refer
Else
raise order
…..
EFD
Level 1
DFD - Examples
14
Wines & Spirits Example
A wines and spirits wholesaler stocks a range of approximately 400
different lines and delivers by van on regular weekly runs to customers
who are mainly off-licenses and clubs. The majority of orders are
received by telephone and any one customer may place several orders
during the week which must be accumulated and delivered in one
consignment. When a customer telephones he expects to be advised on
the availability of an item requested and, if not in stock, the alternatives
that are available. At present, sales order forms are filled in by the
telephone salesmen and sent to the warehouse where they are used for
the despatch of the items. Hand-written despatch notes are used as the
basis of the invoices which are typed and sent by post sometime later.
Prepare a dataflow diagram (DFD) which represents the above system.
DFD - Examples
15
Developing Dataflow Diagrams
1. Identify external entities
2. Draw context diagram
3. Who/Where does what
4. Identify datastores
5. Draw diagram
DFD - Examples
16
External Entities
1. Customer
Context Diagram
order
advice
customer
company
des. note + goods
invoice
DFD - Examples
17
What
Where/who
Receive orders
Sales
Accumulate orders
Sales
Advise availability
Sales
Complete Sales Order Form
Sales
Despatch Items
Warehouse
Write despatch notes
Warehouse
Type Invoices
Warehouse
Send Invoices
Warehouse
Datastore
Stock file
DFD - Examples
18
customer
Draw DFD
Order
Advice
1
Sales
M1
Stock file
Accumulate orders
Advise availability
Complete forms
Sales Order Forms
2
Warehouse
Produce despatch
notes
Produce Invoices
Despatch note +
goods
Invoice
customer
DFD - Examples
19
Extensions
Maintenance of Stock File
Customer file – address, credit etc
Payments
Accounts dept – invoices, payments etc
Accumulate orders – temporary file
DFD - Examples
20
Customer
Draw DFD
Order
Advice
1
Customers
Sales
Stock file
M1
M2
Accumulate orders
Advise availability
Confirm details
Complete forms
Sales Order Forms
Payments
Orders
M3
M4
2
Warehouse
Pick Goods
3
Accounts
Produce Despatch Notes
Copy Dispatch Note
Update Stock File
Produce Invoices
Handle payments
Goods + Copy
Order
Payment
Despatch Note +
Goods
Invoice
Supplier
D/N + Inv
M5
Customer
DFD - Examples
21
Data Dictionary
Name
Alias
Type
Length Max
Custno
Custnum
Num
10
ItemDes
ItemDesc
Alp
20
OrdTot
TotOrd
Cur
5
999
Min
9
e.t.c.
DFD - Examples
22
SELECT (SSADM)
A software package for the development of data flow diagrams and data
models etc.
Comes in various editions to match the methodology used (SSADM)
Check compatibility between DFD and LDS
Checks DFD level compatibility
FREE to copy from library short term loan (need to sign license agreement
and get key from CEMS Help Desk)
DFD - Examples
23
SSADM
Structured
Systems
Analysis
And
Design
Methodology
A highly structured IS development methodology with the emphasis on
analysis and design including the user but little about writing programs,
testing or implementation.
DFD - Examples
24
Fastfood Example
The example below is an illustration of the data flow in a takeaway
restaurant. The order is taken on a carbon pad, the cost is calculated from the
menu, the order is checked with the customer, if OK the order is stuck on a pinboard. When the food is ready, the order becomes the delivery note for the
driver. At the close of business, carbons are used to update accounts and then
dumped along with the delivery notes. Management information is passed to the
manager.
DFD - Examples
25
1
Meal and
Customer details
Record
Order
Meal and
Customer details
D1
Carbon pad
D2
Menu
D3
Pin 1
Look up meal
Customer
Price of meal
2
Record prices
Calculate
Order
New price
Look up prices
Details
3
Re-check
Order
Signature
Manager
Prices
Carbon
details
*second copy goes on Pin2
as a backup
4
Deliver
Order
Daily sales
Current System
D4
Delivery Sheet
D5
Account Book
D6
Pin2
D7
Waste Bin 26
Retrieve
carbon
5
Calculate
All Orders
Fast Food Delivery System
Name, ticket no.and price
Meal total
Retrieve delivery sheet
6
Delete
All Orders
Level 1 DFD
Dump carbon
7
Delete
DFD - Examples
Delivery Sheet
Dump delivery
sheet
Current System – Level 2
Customer
1
Process 1 – Record Order Details
1.1
Record
Meal Details
4
3
2
D1
Carbon Pad
4
1.2
Record
Customer Details
D2
Menu
Fast Food Delivery System
Current System
Level 2 DFD
Notes:
Customer gives meal details (1) and prices are looked up (2)
in the menu before being added (3) to the carbon pad.
Customer details such as address etc. are then added (4) to
the carbon pad.
DFD - Examples
27
Current System – Level 3
Process 1.1 – Record Meal Details
1.1.1
Customer
Add New Meal
to Order
D1
Carbon Pad
D2
Menu
D6
Waste Bin
1
1
1
1.1.2
2
Amend Order
Meal Details
1
1.1.3
Fast Food Delivery System
Current System
Level 3 DFD
Delete
Order
2
Notes:
During a call the customer can simply add meals to her or his
order which go straight onto the carbon pad. However, they could
also change their mind (1) in which case new prices need to be
looked up and the original carbon entry changed. They may even
want to cancel the order (2). Level 2 UNCHANGED data flows are
shown in blue
DFD - Examples
28
Current System – Level 3
Customer
Details
Customer
Process 1.2 – Record Customer Details
1.2.1
Add New
Customer Details
D1
Carbon Pad
Changes to
Customer Details
1.2.2
Amend
Customer Details
Fast Food Delivery System
Current System
Level 3 DFD
Notes:
During a call the customer’s details – name, address etc. are
added to the carbon pad. However, during the call it may be
necessary to amend their details (for example, if the telephone
operator has misheard the original details. Level 2 UNCHANGED
data flows are shown in blue
DFD - Examples
29
Current System – Level 2
Meal
Details
Customer
Process 2 – Calculate Order Value
2.1
Record Meal
Prices
D1
Prices
Total cost
Of meal
Carbon Pad
All
Prices
2.2
Calculate Order
Value
Fast Food Delivery System
Current System
D2
Menu
Notes:
During a call individual meal prices are looked up in the menu and
added to the carbon pad. On completion of an order the prices of
all ordered meals, on the pad, are added together to give the total
cost of the meal. This is then relayed to the customer.
Level 2 DFD
DFD - Examples
30
Current System – Level 2
Meal
Details
Customer
Process 3 – Re-check Order
3.1
Amend Meal
Details
D1
Carbon Pad
D2
Menu
Customer
Details
3.2
New Price
of Order
Amend Customer
Details
3.3
Fast Food Delivery System
Current System
Level 2 DFD
Recalculate
Order
Notes:
After an order is complete the customer may ring up to check they
have given the correct details or to amend an order (forgotten the
prawn crackers!) In this case details on the carbon pad are
checked and amended as necessary before the customer is given
the new price of the order.
DFD - Examples
31
Current System – Level 3
Customer
Process 3.1 – Amend Meal Details
3.1.1
New Meal
Details
Add New Meal
to Order
D1
Carbon Pad
D2
Menu
D7
Waste Bin
Changes to
Ordered Meals
3.1.2
Customer and
Order Details
Amend Order
Meal Details
3.1.3
Fast Food Delivery System
Current System
Level 3 DFD
Delete
Order
Notes:
After an order has been taken the customer may telephone to
amend order details. She could ask to add new meals or amend
meals and prices will have to be looked up in the menu. Or, she
can cancel the order in which case it is consigned to the waste
bin.
DFD - Examples
32
Current System – Level 2
Process 4 – Deliver Order
4.1
Customer
Complete
Delivery Sheet
D3
Pin1
Customer
Signature
4.2
Obtain Customer
Signature
Fast Food Delivery System
Current System
D4
Delivery Sheet
Notes:
When the order is ready for delivery the carbon on Pin1 is used to
complete the drivers delivery sheet – customer details, cost of
order. On delivery of the order the customer is asked to sign the
delivery sheet.
Level 2 DFD
DFD - Examples
33
Current System – Level 2
Process 5 – Calculate All Orders
D3
Manager
Total
Sales
5.1
Pin1
Order
Values
Calculate
All Orders
Total sales
D5
Fast Food Delivery System
Current System
Account Book
Notes:
At the close of business all orders that have been taken during the
day (carbons) are taken from Pin 1 and the total value of daily
business is calculated manually (using a calculator) by the
Accounts person. This information is passed onto the restaurant
manager.
Level 1 DFD
DFD - Examples
34
Current System – Level 2
Process 6 – Delete All Orders
6.1
Delete Original
Copies
D3
Pin 1
D6
Pin 2
D7
Waste Bin
6.2
Delete Duplicate
Copies
Fast Food Delivery System
Current System
Notes:
At the close of business all original and duplicate copies of orders
(carbons) are removed from the pins and disposed of.
Level 2 DFD
DFD - Examples
35