1. Data Flow Diagram
(Design)

2. Overview:-Overview:-
 Data flow diagrams(DFD) are commonly
used during problem analysis.
 DFD is an useful tool for software engg as
well as for the developmnet of other
systems.
 In fact, dfds have in use long before the
discipline of software engg started.

3. Salient features of any DFD:-Salient features of any DFD:-
 DFDs are basically used to show the flow
of data through a system.
 The System may be an organization,a
manual procedure, a software system, a
mechanical system,a hardware system or
any possible combination of these.
 There are several processes in a dfd.
Each process is shown by named
circles(or bubbles).

4. Salient features of any DFD(contd….)Salient features of any DFD(contd….)
 Data flows are represented by named arrows
entering (or leaving) the bubbles.
 A rectangle represents the source which is either
a net originator or consumer of data.
 All external files are shown as a labeled straight
line.
 When multiple data flows are required by a
system this is represented by a ‘*’ between the
data flows.This symbol represents the AND
operation.

5. How is a DFD different from aHow is a DFD different from a
flowchart?flowchart?
 One must always remember that a dfd is not a
flowchart.
 While a DFD represents the “flow of data” a flow
chart shows the “flow of control”.
 A dfd does not represent procedural
information.For eg:- considerations of loops and
decisions must be ignored.
 In drawing the dfd the designer has to specify
what are the major transforms in the flow of the
data from the input to the output.

6. How is a DFD different from aHow is a DFD different from a
flowchart?(contd…)flowchart?(contd…)
 How the transforms are occurring is not
the concern of the designer.
 Error messages are not shown in the dfd.

7. DFDs for large systems(LeveledDFDs for large systems(Leveled
DFDs)DFDs)
 Many systems are too large for a single dfd to
represent the entire data processing clearly.
 So, it becomes necessary that some
decomposition and abstraction mechanisms be
used for such large systems.
 DFDs can be hierarchically organized which
helps in progressive partitioning and analyzing of
large systems.
 Such dfds are called “Leveled DFD set”

8. How to draw a Leveled DFD set?How to draw a Leveled DFD set?
 A leveled DFD set has a starting dfd, which is a
very abstract representation of the system
identifying the major inputs ,outputs and the
major processes in the system.
 Then each process is refined and a dfd is shown
for the corresponding refinements.
 In other words, a bubble in a dfd is expanded
into another dfd during refinement.
 For the hierarchy to be consistent ,it is necessary
that the net inputs and outputs

9. How to draw a Leveled DFD set?(contd…)How to draw a Leveled DFD set?(contd…)
of a dfd for a process are the same as the
inputs and the outputs of the process in
the higher level dfd.
 This refinement stops if each bubble is
considered to be “atomic” ; in that case
each bubble can be easily specified or
understood.
 The top level dfd is sometimes called the
“context-diagram”.

10. Suggestions for DFD construction:-Suggestions for DFD construction:-
 Start with a data flow graph with a few
major transforms describing the entire
transformation form the inputs to the
outputs and then refining each transform
with more detailed transforms.
 We must never try to show the control
logic.If we find ourselves to be thinking in
terms of loops and decisions then it is time
to stop and start again.

11. Suggestions(contd….)Suggestions(contd….)
 Label each arrow with proper data elements and
inputs and outputs of each transform needs to be
carefully identified.
 Make use of ‘*’ and ‘+’ signs and show sufficient
data in the data flow graph.
 Try and draw alternate data flow graphs before
settling on one.
 After drawing the dfd the next step is to establish
a man-machine boundary by specifying what will
be automated and what will remain manual in the
dfd for the new system.

12. Data Dictionary:-Data Dictionary:-
 Data dictionary is almost a data structure
that keeps track of information about data
flows.
 Data dictionary states precisely the
structure of each data flow in the dfd.
 The structure of a data could be defined
with different notations which are almost
similar to those used for regular
expressions.

13. Data Dictionary:-(contd…)
 Some of the commonly used notations are
as below:-
 “+” indicates composition.
 “|” indicates one OR the other.
 “*” indicates one or more occurences.

14. DFD of a System that Pays Workers :
Employee Record Company Records
Weekly Timesheet Tax Rates
Get
Employee
File
Weekly
Pay
Overtime
pay
Deducted
Pay
Issue
Pay
Check
Worker
Overtime
Rate
Overtime
Hours
Regular
Hours
Employee
Id
Pay
Rate
Pay Net
Pay
Total
Pay
Check
Worker

15. Analysis of the dfd system for
payment of worker’s:-
 In this dfd there is one basic input data
flow and that is the weekly time sheet,
which originates form the source
worker.
 The basic output is the paycheck, the
sink for which is also the worker.
 In this system first the employee’s
record is retrieved using the employee
id,which is contained in the timesheet.

16. Analysis of the dfd system for
payment of worker’s:-
 From the employee record the rate of
payment and overtime rate are
obtained.These rates and the regular
overtime hours(from the timesheet) are
used to compute the pay.
 After the total pay is determined,taxes are
deducted.

17. Analysis of the dfd system for
payment of worker’s:-
 To compute the tax deduction,information
from the tax-rate file is used.The amount
of tax deducted is recorded in the
company and employee records.
 Finally the paycheck is issued for the net-
pay.The amount paid is also recorded in
the company records.

18. A sample Data dictionary:-
 The data dictionary for the problem involving the
payment of workers is as below:-
 Weekly
timesheet=Employee_name+Employee_id+
[Regular Hours+Overtime Hours]*
 Pay_rate=[Hourly|daily|weekly]+Dollar_Amount
 Employee_name=First+Middle+Last
 Employee_id=digit+digit+digit+digit

19. An Example :A restaurant SystemAn Example :A restaurant System
A restaurant owner felts that some amount
of automation will help him in making the
business more efficient .
DIFFERENT PARTIES INVOLVED:
CLIENT: The Restaurant Owner
POTENTIAL USER: Waiter, Cash register
Operator

20. DFD of a Restaurant System
Supply
Information
Member
Sale
Information
Restaurant
Supplier
Customer
Supply
OrderOfSupplier
Paym
ent
O
rders
Receipt
Final Bill
Several Bill

21. Data Flow Diagram of Spell Check Problem:Data Flow Diagram of Spell Check Problem:
New Dictionary
Misspelled
Word
Get File
Name
Split the
Words
Sort
Words
Lookup
Dictionary
Handle
Unknown
Word
User
Command
FileName
Document
W
ord
List
Sorted
W
ordList
Dictionary
Word not
In
Dictionary
Dictionary
Good
Words
Bad
Words

22. Problem 2:Problem 2:
Library System:Library System:
Needs
Books
Checks
The
Collection
Arranges
Signed on
The card
DeliverReadsReturnsRecollect
File name
Reader
Preferable
Book
Librarian
Books
The
Particular
Book
Library
Card
Selected
BookReader
Library
card
Books

23. Jackson Structure
Programming
(JSP)

24. Jagson’s Structured
Programming(JSP):-
 JSP is a systematic technique for mapping the
structure of any problem into a program
structure.
 The 3 steps for construction of any JSP are:-
 To draw the “data structure diagram” for each
data set.
 Form a “program structure diagram” from the
data structure diagram.
 List all “operations” ,”functional components” and
“conditions”.

25. JSP for Account Processing System:-
FILE
CUSTOMERS
ACCOUNTS TRANSACTIONS
WITHDRAWL DEPOSIT

26. Data Structure Diagram:
Transaction File
File Header File Body End of File Masker
Customer
Accounts
Account Header Account Body
Transaction
Deposit With Drawal

27. Program Structure Diagram
ProcessProcess TransactionTransaction
FileFile
Program StartProgram Start
(1,3)(1,3)
Program BodyProgram Body
(c1)(c1)
Program EndProgram End
(2,6)(2,6)
Process CustomerProcess Customer
(c1 or c2)(c1 or c2)
Process Customer StartProcess Customer Start
(7)(7)
Process Customer BodyProcess Customer Body
Process accountProcess account
Process Account StartProcess Account Start
(3,8)(3,8)
Process Account BodyProcess Account Body
(c1 or c2 or c3)(c1 or c2 or c3)
Process TransactionProcess Transaction
Process DepositProcess Deposit
(3,4)(3,4)
Process WithdrawalProcess Withdrawal
(3,5)(3,5)

28. Operations:-
1. Open Transaction File.
2. Close Transaction File.
3. Read a Record form the file.
4. Add Amount deposited to the total amount.
5. Add amount withdrawn to the total amount.
6. Output the two totals.
7. Set Current Cust_no Cust_no
8. Set Current Acct_no Account_no

29. Conditions:-
 C1 EOF
 C2 Cust_no = Current Cust_no
 C3 Acct_no = Current Acct_no
 C4 Deposit
 C4 WithDrawal

30. JSP for Spelling Checker’sJSP for Spelling Checker’s
Problem:-Problem:-
 Components:-
a)Document File
b)Dictionary File
c)Mispelled Words File
 Conditions:-
C1 EOF

31. Spell Check Problem
This problem took each word used in a
document and in a dictionary. If a word
appears in the dictionary then the word is
correct .Otherwise it is displayed in the
user terminal, The user then decides if the
word is misspelled ,the word is held in a
file of misspelled words and if correctly
spelled then it is added to the dictionary

32. Procedure of Spell check problem:
Begin
loop
get next word
add word to word list in sorted
order
end from the loop when all word
are processed
endloop

33. contdcontd……..……..
loop
get word from sorted word list
If word is not in dictionary then
display the word and prompt
on the user terminal
if user response says word ok then
add word to the dictionary
else
add word to misspelled word list
end if

34. ContdContd
end if
exit when all words are processed
end loop
end

35. Document Misspelled Word List
Dictionary New Dictionary
Basic diagram of Spell Check Problem
Spell check
Problem
T1
Sorting
T2
Dictionary

36. Data Structure Diagram Of Spell Check
Problem
MisspelledMisspelled
WordWord
FileFile
FileFile
HeaderHeader
FileFile
BodyBody
EOFEOF
MarkerMarker
MisspelledMisspelled
WordWord **
GoodGood
WordWord
BadBad
WordWord
DocumentDocument
FileFile
FileFile
HeaderHeader
FileFile
BodyBody
EOFEOF
MarkerMarker
WordWord
DictionaryDictionary
FileFile
FileFile
HeaderHeader
FileFile
BodyBody
EOFEOF
MarkerMarker
MeaningfulMeaningful
WordWord

37. Program Structure Diagram Of Spell Check Problem
ProcessProcess
Spell CheckSpell Check
Program startProgram start
(1)(1)
Program BodyProgram Body
(c1)(c1)
Program EndProgram End
(2)(2)
ProcessProcess
DocumentDocument **
Start DocumentStart Document
Process(3,4)Process(3,4)
Document ProcessDocument Process
BodyBody
ProcessProcess
WordWord **
Start ProcessStart Process
WordWord
Process WordProcess Word
BodyBody
ProcessProcess
DocumentDocument **

38. Cont…
Process DictionaryProcess Dictionary
**
Start DictionaryStart Dictionary
Process(5)Process(5)
Dictionary ProcessDictionary Process
BodyBody
Process MisspelledProcess Misspelled
Word *Word *
Start Misspelled WordStart Misspelled Word
Process(6,7)Process(6,7)
Misspelled WordMisspelled Word
Process BodyProcess Body
Good WordGood Word
(3)(3)
Bad WordBad Word
(8)(8)
Process DictionaryProcess Dictionary
(9)(9)

39. Operations:-
1. Open document file and dictionary.
2. Split the document into words.
3. Sort the words.
4. Lookup the sorted words in the dictionary.
5. Collect the mis-spelt words or output them.
6. Add mis-spelt words to mis-spelt word list.
7. Identify good words form mis-spelt words.
8. Add good words to the dictionary.
9. Output the bad words to the user.
10. Close the file.

40. Bank Problem:-
A problem is received to process Bank transaction
keyed in at a terminal .The Program is to be
menu driven & the menu gives user three
option
1. Input of deposit
2. For input of withdrawal
3. Terminate program ( option-9)
Deposit are to be written to the deposit file and
withdraw are to be written in withdrawal file.
Additionally file trailers are to be appended to
deposit and withdrawal file containing the total
deposit and withdraw respectively

41. Data Structure Diagram of Bank Transaction
(Screen Data Structure Diagram)
Screen InputScreen Input
(1)(1)
Input BodyInput Body
(2)(2)
Option-9Option-9
Terminate(3)Terminate(3)
MenuMenu **
Option -1Option -1
Deposit (4)Deposit (4)
Option -2Option -2
Withdraw (4)Withdraw (4)
InvalidInvalid
OptionOption

42. Data Structure Diagram Of Deposit File and Withdrawal
File
Deposit FileDeposit File
(1)(1)
File BodyFile Body
(2)(2)
File TrailerFile Trailer
(3)(3)
DepositDeposit **
(4)(4)
Withdrawal FileWithdrawal File
(1)(1)
File BodyFile Body
(2)(2)
File TrailerFile Trailer
(3)(3)
WithdrawalWithdrawal **
(5)(5)

43. Program Structure Diagram of Bank
Transaction Problem
Process Screen
Input
Program Start
(1,3,4,5)
Program Body
(c3)
Program End
(2,13,14)
Process *
Menu
Process Menu
Body(c1,c2)
Process Menu
End
Process Option-1
Deposit
(7,9,11)
Process Option-2
Withdrawal
(8.10.12)
Process

44. Data Structure Diagram of File copy Problem
INFILE 1INFILE 1
INFILE 1INFILE 1 ** INFILE 2INFILE 2 **
INFILE 2INFILE 2

45. Program structure Diagram of File Copy
Copy INFILE1 ToCopy INFILE1 To
INFILE2INFILE2
Program StartProgram Start
(1,3)(1,3)
Program BodyProgram Body
(C1)(C1)
Program EndProgram End
(2)(2)
Copy INFILE1 ToCopy INFILE1 To
INFILE 2INFILE 2
(3,4,5)(3,4,5)