DFD - Examples 1

Data Flow Diagrams - Examples

And Franchise Colleges

By MANSHA NAWAZ

Using SSADAM Notation

DFD - Examples 2

CompanyCustomer

Despatch Note + Goods

Order

Rejected Order

Context Diagram

DFD - Examples 3

Customer

Sales1Order

Rejected Order

Dispatch Note

2 Warehouse

Dispatch Goods

3 Accounts

Maintain Credit Ratings

D1 Credit Rating

Check Credit Rating

A Complete DFD

DFD - Examples 4

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 5

Customer

Sales

Check Credit Rating

D1 Credit Rating

A Data Flow

An External Entity

A Process

A Data Store

3

DFD Symbols

SSADM Notation

DFD - Examples 6

Sales

Check Credit Rating

3

Unique Number Where it’s done

What’s done

Output DataInput Data

The Process Symbol

DFD - Examples 7

Accounts

Maintain Credit Rating

3

Sales

Check Credit Rating

1

M = Manual data Store

D = Computer File

D1 Credit Rating

Writing/Updating

Reading

The data store symbol

DFD - Examples 8

Sales

Check Credit Rating

3

D1 Credit Rating

The Data Flow Symbol

Customer Balance

Use Meaningful names

Self Evident Data Flows need

not be named

DFD - Examples 9

Physical Resource Flow

Customer

Returned

Library Book

DFD - Examples 10

The External Entity Symbol

Customer

System Boundary

A Source and/or sink of data outside the system boundry

DFD - Examples 11

2 Dispatch Goods

2

1

Process

2.1

Dispatch

Note

Validated

Order

Levelling – to avoid complex DFDs, processes can be grouped into higher level processes

DFD - Examples 12

Customer

Sales1Order

Rejected Order

Dispatch Note

2 Warehouse

Dispatch Goods

3 Accounts

Maintain Credit Ratings

D1 Credit Rating

Check Credit Rating

A Complete DFD

DFD - Examples 13

Customer

D1 Credit Rating

A Duplicated External Entity

Duplicated Data Store

Customer

Repeated Symbols – to avoid crossing lines, data

stores and external entities can be repeated:

DFD - Examples 14Level 1

Level 2

E F D

Elementary

Functional

Description

Get cust dets

If order>cred

refer

Else

raise order

…..

DFD Levels

DFD - Examples 15

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 16

Developing Dataflow Diagrams

1. Identify external entities

2. Draw context diagram

3. Who/Where does what

4. Identify datastores

5. Draw diagram

DFD - Examples 17

External Entities

1. Customer

Context Diagram

customer company

order

invoice

advice

des. note + goods

DFD - Examples 18

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 19

customer

customer

Stock file

Accumulate orders

Advise availability

Complete forms

1 Sales

Sales Order Forms

2

Produce despatch notes

Produce Invoices

InvoiceDespatch note + goods

Warehouse

Draw DFD

OrderAdvice

M1

DFD - Examples 20

Extensions

Maintenance of Stock File

Customer file – address, credit etc

Payments

Accounts dept – invoices, payments etc

Accumulate orders – temporary file

DFD - Examples 21

Customer

Customer

Stock file

Accumulate orders

Advise availability

Complete forms

1 Sales

Sales Order Forms

2

Pick Goods

Produce Despatch Notes

Update Stock File

Invoice

Despatch Note + Goods

Warehouse

Draw DFD

OrderAdvice

M1

3

Produce Invoices

Handle payments

Accounts

M4M3

M2

Payments

Customers

Confirm details

Supplier

Goods + Copy Order

Orders

Payment

Copy Dispatch Note

M5D/N + Inv

DFD - Examples 22

Data Dictionary

Name Alias Type Length Max Min

Custno CustnumNum 10

ItemDes ItemDesc Alp 20

OrdTot TotOrd Cur 5 999 9

e.t.c.

DFD - Examples 23

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 24

Structured

Systems

Analysis

And

Design

Methodology

SSADM

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 25

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 pin-board.  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 26

DeleteAll Orders

Re-checkOrder

DeliverOrder

CalculateAll Orders

RecordOrder

CalculateOrder

DeleteDelivery Sheet

1

2

3

4

5

6

7

Carbon pad

Menu

Pin 1

Delivery Sheet

Waste Bin

Customer

Meal and Customer details

Price of meal

New price

Details

Signature

Meal and Customer details

Look up meal

Record prices

Prices

Look up prices

Name, ticket no.and price

Dump carbon

Meal total

Retrieve delivery sheet

Dump deliverysheet

Carbondetails

Retrievecarbon

D1

D2

D3

D4

Account BookD5

D7

Fast Food Delivery System

Current System

Level 1 DFD

*second copy goes on Pin2as a backup

Pin2D6

Manager

Daily sales

DFD - Examples 27

Customer

Menu

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.

Fast Food Delivery System

Current System

Level 2 DFD

1

4

3

2 4

Current System – Level 2 Process 1 – Record Order Details

Carbon PadD1

D2

RecordMeal Details

1.1

RecordCustomer Details

1.2

DFD - Examples 28

Current System – Level 3 Process 1.1 – Record Meal Details

Customer Add New Mealto Order

1.1.1

Amend OrderMeal Details

1.1.2

DeleteOrder

1.1.3

Fast Food Delivery System

Current System

Level 3 DFD

Carbon PadD1

MenuD2

Waste BinD6

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

11

1

12

2

DFD - Examples 29

Current System – Level 3 Process 1.2 – Record Customer Details

Customer Add NewCustomer Details

1.2.1

AmendCustomer Details

1.2.2

Fast Food Delivery System

Current System

Level 3 DFD

Carbon PadD1

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

Changes toCustomer Details

CustomerDetails

DFD - Examples 30

Current System – Level 2 Process 2 – Calculate Order Value

Customer Record MealPrices

2.1

Calculate OrderValue

2.2

Fast Food Delivery System

Current System

Level 2 DFD

Carbon PadD1

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.

MealDetails

Total costOf meal

MenuD2

Prices AllPrices

DFD - Examples 31

Current System – Level 2 Process 3 – Re-check Order

Customer Amend MealDetails

3.1

Amend CustomerDetails

3.2

RecalculateOrder

3.3

Fast Food Delivery System

Current System

Level 2 DFD

Carbon PadD1

MenuD2

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.

MealDetails

CustomerDetails

New Priceof Order

DFD - Examples 32

Current System – Level 3 Process 3.1 – Amend Meal Details

Customer Add New Mealto Order

3.1.1

Amend OrderMeal Details

3.1.2

DeleteOrder

3.1.3

Fast Food Delivery System

Current System

Level 3 DFD

Carbon PadD1

MenuD2

Waste BinD7

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.

Changes toOrdered Meals

Customer andOrder Details

New MealDetails

DFD - Examples 33

Current System – Level 2 Process 4 – Deliver Order

Customer CompleteDelivery Sheet

4.1

Obtain CustomerSignature

4.2

Fast Food Delivery System

Current System

Level 2 DFD

Pin1D3

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.

Delivery SheetD4

CustomerSignature

DFD - Examples 34

Current System – Level 2 Process 5 – Calculate All Orders

Fast Food Delivery System

Current System

Level 1 DFD

CalculateAll Orders

5.1

Pin1D3

Account BookD5

TotalSales

Total sales

OrderValues

Manager

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.

DFD - Examples 35

Current System – Level 2 Process 6 – Delete All Orders

Delete OriginalCopies

6.1

Delete DuplicateCopies

6.2

Fast Food Delivery System

Current System

Level 2 DFD

Pin 1D3

Pin 2D6

Waste BinD7

Notes:At the close of business all original and duplicate copies of orders (carbons) are removed from the pins and disposed of.