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;
Process
•The data flow;
•The external entity.
Entity
Data flow
Data flow
Entity
Entity
Process
A context diagram
URL
Keyword
Student
Use
Search
engine
Student searches the internet
A context diagram
Student
Create a context diagram for:
1.Searching an online telephone
database.
2.Use of an ATM.
3.Use self server check out.
DFD
DFD
DFD
DFD
DFD
DFD
DFD
DFD
A DFD is a graphical method of
Representing a system using a number of
processes together with
•
inputs;
•
outputs;
•
storage.
The 4 main symbols used to show :
the process;
Process
the data flow;
the data store;
Data
Database
the external entity.
store
External
Entity
Call details
Customer
Search
Customer
details
Call number
details
Database
A data flow diagram
invoice
Customer
Order is
processed
Customer
order
Customer & order details
Invoice & book
Database
invoice is generated
and sent
A data flow diagram
URL
Use search
engine
student
Load website
keyword
URL
keyword
Database
Of website
graphic
Project
A data flow diagram search for image
A video store is considering installing a ‘self-checkout’ system where customers
can borrow videos by scanning their membership cards and videos and pay by
EFTPOS.
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 to
access the member database to find a match. The customer proceeds to the
scanning 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 scanning
of the customer’s EFTPOS card, the entry of a personal identification number
and 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 ‘selfcheckout’ 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:
Entity
Processes
borrower Search d/b of borrowers
for borrowing eligibility
Search d/b for details of
requested book
Locate book, scan book
& user bar code
Update borrower &
book records
Storage
D/b of borrowers, books
& library transactions
Data flow
Borrowers details
& book request
Information about
borrower
Information about
books
Information about
library transactions
Result of d/b
search
6
10
1
Process
Database
7
2
Process
9
5
3
8
Process
borrower
6
4
Process
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 customers
can borrow videos by scanning their membership cards and videos and pay by
EFTPOS.
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 to
access the member database to find a match. The customer proceeds to the
scanning 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 scanning
of the customer’s EFTPOS card, the entry of a personal identification number
and 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 ‘selfcheckout’ system, ensuring that you show
external entities and data stores. (Refer
standards package section 2 Q.25)
Link to dfd tutorials
http://www.getahead-direct.com/gwbadfd.htm
http://www.agilemodeling.com/artifacts/dataFlowDiagram.htm
http://www.cems.uwe.ac.uk/~tdrewry/dfds.htm
http://spot.colorado.edu/~kozar/DFDtechnique.html
http://www.infoarchgroup.com/qrdfd.htm
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.
Symbol
Meaning
Symbol Meaning
Input/output
Manual operation
Paper
document
Magnetic tape
Online display
Direct access
storage device
Online input
Flowline
Punched cards
Telecommunication
link
Process
Terminal
Predefined process
Decision
A system flow chart for finding a book in the library.
begin
Enter book
details
Library software
Library database
Search results
False
False
Need printout
Are you finished
True
End
True
Search report
A system flow chart for hardware
Colour inkjet
printer
Keyboard
Laptop
Scanner
Internet
CD-Rom
drive
Floppy
drive
Zip drive
modem
Network
connection
Mouse
File server
Input
Processing
Output