Context &

Dataflow

Diagrams

CONTEXT DIAGRAM

A context diagram is a graphical method of representing using a single process together with inputs and outputs (external entities)

Three symbols only exist•The process;

•The data flow;

•The external entity.Entity

Process

Entity Process

EntityData flowData flow

A context diagram

Student

UseSearch engine

StudentKeywordURL

A context diagram

Student searches the internet

Create a context diagram for:

1.Searching an online telephone database.

2.Use of an ATM.3.Use self server check out.

DFD

DFD

DFDDFD

DFD

DFDDFD

DFD

A DFD is a graphical method of Representing a system using a number of processes together with • inputs; • outputs; • storage.

Process

The 4 main symbols used to show : the process;

the data flow;

the data store;

the external entity.

DatabaseDatastore

ExternalEntity

Customer

SearchCustomer

details

details Call number

Call details

A data flow diagram

Database

Customer

Order is processed

Customer

order

Invoice & book

Customer & order details

invoice

A data flow diagram

Database invoice is generated

and sent

student

Use searchengine

Load website

DatabaseOf website

keyword

keywordURL

URL

A data flow diagram search for image

Project

graphic

A video store is considering installing a ‘self-checkout’ system where customerscan borrow videos by scanning their membership cards and videos and pay byEFTPOS.

A ‘self-checkout’ transaction has three steps:• membership validation;• borrowing limit check;• payment processing.

For membership validation the barcode on the membership card is used toaccess the member database to find a match. The customer proceeds to thescanning of videos if the membership is valid, otherwise a message is displayed.

Using the video barcode data and details from the member database, the system checks that no more than six videos are borrowed. A message is displayed if the limit is exceeded.

Payment processing involves the calculation of borrowing charges, the scanningof the customer’s EFTPOS card, the entry of a personal identification numberand the electronic communication of these details to the financial institution.Video charges are obtained from the video database via the video barcodes.Transaction details are written to the transaction file for each video borrowed.

(i) Draw a dataflow diagram with the three processes that represents this proposed ‘self-checkout’ system, ensuring that you show external entities and data stores. (Refer standards package section 2 Q.25)

Create a data flow diagram for the borrowing of a book.

STEPS I TAKE WHEN CREATING SUCH A TOOL.

1. Decide upon the:• processes , • entities, • dataflow • storage.2. Draw rough diagram adding the:• processes , • entities, • dataflow • storage.3. Label as you go.

Create a data flow diagram for the borrowing of a book:

EntityEntity ProcessesProcesses Data flowData flow

borrowerborrower Search d/b of borrowers Search d/b of borrowers for borrowing eligibilityfor borrowing eligibility

Borrowers details & Borrowers details & book requestbook request

Search d/b for details of Search d/b for details of requested bookrequested book

Information about Information about borrowerborrower

Locate book, scan book Locate book, scan book & user bar code& user bar code

Information about Information about booksbooks

Update borrower & book Update borrower & book recordsrecords

Information about Information about library transactionslibrary transactions

Result of d/b Result of d/b searchsearch

StorageStorage D/b of borrowers, books D/b of borrowers, books & library transactions& library transactions

Process

Process

Process

Process

borrower

Database1

2

3

4

5

6

7

89

10

6

Create a data flow diagram for:

1.Searching an online telephone database.

2.Use of an ATM.3.Use self server check out.

A video store is considering installing a ‘self-checkout’ system where customerscan borrow videos by scanning their membership cards and videos and pay byEFTPOS.

A ‘self-checkout’ transaction has three steps:• membership validation;• borrowing limit check;• payment processing.

For membership validation the barcode on the membership card is used toaccess the member database to find a match. The customer proceeds to thescanning of videos if the membership is valid, otherwise a message is displayed.

Using the video barcode data and details from the member database, the system checks that no more than six videos are borrowed. A message is displayed if the limit is exceeded.

Payment processing involves the calculation of borrowing charges, the scanningof the customer’s EFTPOS card, the entry of a personal identification numberand the electronic communication of these details to the financial institution.Video charges are obtained from the video database via the video barcodes.Transaction details are written to the transaction file for each video borrowed.

(i) Draw a dataflow diagram with the three processes that represents this proposed ‘self-checkout’ system, ensuring that you show external entities and data stores. (Refer standards package section 2 Q.25)

http://www.getahead-direct.com/gwbadfd.htmhttp://www.agilemodeling.com/artifacts/dataFlowDiagram.htmhttp://www.cems.uwe.ac.uk/~tdrewry/dfds.htmhttp://spot.colorado.edu/~kozar/DFDtechnique.htmlhttp://www.infoarchgroup.com/qrdfd.htm

Link to dfd tutorials

Systems Flow Chart

Systems flow chart is a graphical method of representing both the flow of data and the logic of the system.

It documents the essential details of the system such as sequence, processes and precise rules for selecting particular actions.

The flow chart will also show the hardware used to process data, such as the peripheral devices, storage media and processing units.

SymbolSymbol MeaningMeaning SymbolSymbol MeaningMeaning

Input/outputInput/output Manual operationManual operation

Paper Paper documentdocument Magnetic tapeMagnetic tape

Online displayOnline display Direct access storage Direct access storage devicedevice

Online inputOnline input Flowline Flowline

Punched cardsPunched cards Telecommunication Telecommunication linklink

ProcessProcessPredefined processPredefined process

TerminalTerminal DecisionDecision

begin

Enter bookdetails

Library software

Search results

Need printoutFalse True

False

True

Search report

Are you finished

End

Library database

A system flow chart for finding a book in the library.

A system flow chart for hardware

Laptop

Zip drive

Floppy drive

CD-Rom drive

Colour inkjet printer

Keyboard

Scanner

Mouse

Input Processing Output

modemNetwork

connection

File server

Internet