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
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