Systems Analysis and Design Bachelor of Information Technology External Degree Programme by Kapila D

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Program Design
Fundamentals of Programming IT1202
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Learning Management System (LMS)

• Submission Deadlines
• First two sets of Quizzes 17-Nov-03
• Assignment 1 (Individual) 01-Dec-03
• Assignment 1 (Group) 15-Dec-03
• Second two sets of Quizzes 29-Dec-03
• Assignment 2 (Individual) 12-Jan-04
• Assignment 2 (Group) 26-Jan-04
• Seminar Questions 09-Feb-04

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An overview of program design

• Importance of professional programming
• In most cases , used for large and complex
  systems
• Maintained by people other than the original
  author
• Last for many years and continually enhanced and
  amended to meet the changing environment

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Evolution of Program Design

• Programming as an Art Form
• Some forty years ago , the main preoccupation was
  with the correctness of the solution
• The design tool that emerged from this period was
  the flowchart
• Main concern was with logic flow

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Evolution of Program Design..

• Modular Programming
• In early 60s, program designers stressed the
  importance of modular programming
• This was a process of top-down decomposition
• Main concern was with the structure of the
  program as well as the logic flow

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Evolution of Program Design

• Structured Programming
• In 1966 Bohm and Jacopini demonstrated that
  any program can be constructed using three
  constructs
• Sequence
• Selection
• Iteration

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Evolution of Program Design

• Object-Oriented Programming (OOP)
• Emerging major programming paradigm
• Main concern is an Object which is a
  particular instance of a class which consist of
• Data
• Methods

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Main components of a Program

• Program Data Algorithm
• Data Basic Facts such as Name, Date of Birth,
  Telephone Number, Address which we process
  through a program
• An algorithm is an effective procedure for
  solving a problem in a finite number of steps

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Important Features of Data

• Data Names
• Implicit Explicit Data
• Data Types
• Usage of Data
• Data Structures
• Scope of Data

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Important Features of Data.

• Data Names
• All programming languages have rules when giving
  names to data items
• No of characters to be used
• Type of characters to be used
• e.g. we can give alphabetic characters ,
  , etc.
• Whether they are case sensitive
• Whether the characters used imply any special
  characteristics

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Important Features of Data

• Explicit vs. implicit definition of data
• Total Total Counter

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Important Features of Data..

• Data types
• Numeric data
• Integers Eg. 3
• Real Numbers - Eg. 5.5
• Character data - Eg. x
• Boolean data Eg. Yes or no
• Data usage
• Variables can be changed
• Constants can not be changed

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Important Features of Data..

• Data structures
• Single items
• (No contained sub-items)
• e.g.
• total , counter

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Important Features of Data

• Data structures
• Structured items (group items)
• Has a number of sub-parts
• eg a persons name contain a given name a
  family name
• Classified under two types
• A record
• An array

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Important Features of Data .

• A record
• A structure in which each part has an identifying
  name
• Data contained in each part of the record may be
  accessed by referring to that name
• eg define StudentRecord as
• IdNumber integer
• Name string
• Address string
• DateOf Birth string
• FeePayable real
• end define

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Important Features of Data

• An array
• Consist of sub components which has the same name
  and are accessed by giving their position within
  the array
• The sub components are normally required to be
  all of the same type size.
• e.g. DailyRainfall(365) real
• This array consist of 365 real numbers

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Important Features of Data..

• Data scope
• Global
• Accessible by a number of procedures/functions
• Defined within an outer procedure may then be
  shared by the inner procedures
• The ability for a number of procedures to share
  global data removes the need to pass the data
  from one procedure to another
• However there is a possibility to corrupt the
  data by sharing global data
• Should be used warily within a program

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Important Features of Data

• Local
• Defined within a procedure for access by that
  procedure only
• Keep data private within any procedure and avoid
  possible corruption by other procedures
• Enable a procedure to be encapsulated
• It is possible for a number of procedures to have
  a variable having the same name

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• Simple procedures/functions
• A program is a series of procedures/functions
• designed to process data
• produce a result according to a problem
  specification

Proc One
Proc two
Proc n
Program
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An example of an algorithm for making a pot of tea

• If the kettle does not contain water then fill
  the kettle
• Plug the kettle into the power point and switch
  it on
• If the tea pot is not empty then empty the teapot
• Place tea leaves in the teapot
• Check whether water is boiling in the kettle
• If the water in the kettle is not boiling then go
  to step 5
• Switch off the kettle
• Pour water from the kettle into the teapot

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An example of an algorithm for making a pot of
tea.

• If the kettle does not contain water then fill
  the kettle
• Plug the kettle into the power point and switch
  it on
• If the tea pot is not empty then empty the teapot
• Place tea leaves in the teapot
• Check whether water is boiling in the kettle
• If the water in the kettle is not boiling then go
  to step 5
• Switch the kettle off
• Pour water from the kettle into the teapot

Sequence
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An example of an algorithm for making a pot of
tea.

• If the kettle does not contain water then fill
  the kettle
• Plug the kettle into the power point and switch
  it on.
• If the tea pot is not empty then empty the teapot
• Place tea leaves in the teapot
• Check whether water is boiling in the kettle
• If the water in the kettle is not boiling then go
  to step 5
• Switch the kettle off
• Pour water from the kettle into the teapot

Selection
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An example of an algorithm for making a pot of
tea.

• If the kettle does not contain water then fill
  the kettle
• Plug the kettle into the power point and switch
  it on.
• If the tea pot is not empty then empty the teapot
• Place tea leaves in the teapot
• Check whether water is boiling in the kettle
• If the water in the kettle is not boiling then go
  to step 5
• Switch the kettle off
• Pour water from the kettle into the teapot

Repetition
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What is a computer program

• The computer scientist Niklaus Wirth
• stated that
• Program Data Algorithm
• We can say
• sequence of instructions which the CPU
  interprets as arithmetical and logical operations
  

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Tools for Algorithm Design
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A good design tool will lead to programs which
are

• Concise
• Capable of machine execution
• Accurate in their operation
• Easy to amend and enhance over a long period of
  time
• Must promote elegance in the solution
• Unambiguous

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Different Tools available

• Flowcharts
• Nassi-shneiderman (NS) Diagrams
• Pseudocode

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What is a flow chart

• Diagrammatic representation of the algorithm
• Many symbols are included in its notation

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Notations for flow charts

• Process or operation

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Notations for flow charts.

• Decision

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Notations for flow charts.

• Terminator

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Notations for flow charts

• Flow of logic

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What is NS diagram

• Use to illustrate the flow of logic of a problem
• Use different pictures to represent the logic of
  a program

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What is a NS diagram..

• The flow of logic is indicated by joining the
  symbols together
• Steps are executed from top to bottom
• No arrows are used to indicate the flow

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Notations for NS diagrams

• Process

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Notations for NS diagrams..

• Decision

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Notations for NS diagrams..

• Iteration

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Notations for NS diagrams..

• A called sub-procedure

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What is Pseudocode

• Text based tool rather than a diagrammatic one
• Some times called Structured English
• Algorithm is specified with the same precision as
  that of the programming language to be used
• There is no universal pseudocode

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Key words used in Pseudocode

• global
• Global data
• local
• Local data
• input
• Data to be entered through the Key board
• display
• Screen output

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Key words used in Pseudocode

• Comments
• E.g. This is a comment
• stop
• Termination of execution
• Assignment of value

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Key words used in Pseudocode

• Arithmetic operators
• exponentiate
• multiply
• add
• / divide
• - subtract
• () to vary the order of precedence

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Sequence controls used in Pseudocode

• Selection

if condition(s) then statement(s) else
statement(s) end if
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Sequence controls used in Pseudocode

• Multiple selection

Case of data-name value statement(s)
else statements(s) end case
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Sequence controls used in Pseudocode

• Leading test loop ( repetition)

while condition(s) statement(s) end while
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Sequence controls used in Pseudocode

• Trailing test loop ( repetition)

repeat statement(s) until condition(s) end
repeat
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Algorithm specification

• Now lets take one problem and try to
  illustrate with different tools discussed

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Problem One
Pseudocode

• if mark gt 75 then
• display D
• else
• if mark gt 60 then
• display C
• else
• if mark gt 40 then
• display S
• else
• display F
• end if
• end if
• end if

This is an example of a nested if condition
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Problem One
NS diagram
mark gt 75
Y
N
mark gt 60
Y
N
Display D
Y
N
mark gt 40
Display C
Display S
Display F
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Problem One
Flow charts
markgt75
YES
NO
display D
markgt60
NO
YES
display C
NO
mark gt 40
YES
display S
display F
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Problem Two
Pseudocode

• X 0
• while X lt 10
• display X
• X X 1
• end while

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Problem Two
NS Diagram
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Problem Two
Flow Charts
X 0
FALSE
Is X lt 10?
TRUE
X x 1
Display X
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• Comparison of certain features of Design Tools

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Some Useful URLs

• Importance of professional programming
• http//www.overthenet.com/programming.html
• Tools for program Design
• http//mime1.gtri.gatech.edu/MM_Tools/design.html
• Evolution of software design
• http//homepages.feis.herts.ac.uk/nehaniv/al7ev/n
  ehaniv-intro/node9.html
• Tools for algorithm specification comparison
  between them
• http//www.gcseguide.co.uk/flow_charts.htm
• Describes about flow charts
• http//dragon.herts.ac.uk/study/modules/mele0006/s
  trucds2.htm
• Data names
• http//java.sun.com/docs/books/tutorial/java/nutsa
  ndbolts/variables.html

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Some Useful URLs

• Data names
• http//java.sun.com/docs/books/tutorial/java/nutsa
  ndbolts/variables.html
• Explicit vs. implicit definition of data
• http//www.zvon.org/tmRFC/RFC971/Output/chapter3.h
  tml
• Data types data usage
• http//java.sun.com/docs/books/tutorial/java/nutsa
  ndbolts/datatypes.html
• Describe the data types
• http//www.rational.com/centers/data_usage/index.j
  sp?SMSESSIONNO
• Data structures
•  http//www.cs.sunysb.edu/skiena/214/lectures/lec
  t1/lect1.html