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MODULE:I

INTRODUCTIONTO

SOFTWARE ENGINEERING

3/1/2011 1MODULE:I INTRODUCTION TO SOFTWAREENGINEERING

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Software Engineering

Software engineering (SE) is a professiondedicated to designing, implementing, andmodifying software so that it is of higher

quality, more affordable, maintainable, andfaster to build.

Systematic collection of past experience:

Techniques, Methodologies,

Guidelines.


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The IEEE Definition

TheIEEE Computer Society'sSoftware Engineering

Body of Knowledge defines "softwareengineering"

astheapplicationofasystematic,disciplined,

quantifiableapproachtothedevelopment,operation,andmaintenanceofsoftware,andthe

studyoftheseapproaches;thatis,theapplicationof

engineering tosoftware.

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Why Study Software Engineering? (1)

To acquire skills to develop large programs

Exponential growth in complexityand difficulty level with size.

The ad hoc approach breaks down

when size of software increases.


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Ability to solve complex programmingproblems:

How to break large projects into smallerand manageable parts?

How to use abstraction?

Also learn techniques of:

Specification, design, user interfacedevelopment, testing, projectmanagement, etc.


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To acquire skills to be a better programmer:

- Higher Productivity

- Better Quality Programs


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PROGRAM vs SOFTWARE

PROGRAM

Usually small in size

Author himself is sole user

Single developer

Lacks proper user interface

Lacks proper

documentation

Ad hoc development.

SOFTWARE

Large

Large number of users

Team of developers

Well-designed interface

Well documented & user-

manual prepared

Systematic development


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SOFTWARE

Software consists of three components:

-Program ,whenexecutedprovidesdesiredfunctionandperformance.

-Documents ,thatdescribetheoperationandtheuseofprogram.

-Data structure ,thatenabletheprogramstoadequatelymanipulateinformation.

In other words software is the collection ofcomputer programs ,procedure rules andassociated documentation and data.


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Softwares Dual Role

Software is a product

Deliverscomputing potential

Produces,manages,acquires,modifies,displays,or

transmitsinformation

Software is a vehicle for delivering a product

Supports ordirectlyprovidessystemfunctionality

Controls otherprograms(e.g.,anoperatingsystem) Effectscommunications (e.g.,networkingsoftware)

Helpsbuild othersoftware(e.g.,softwaretools)


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Types of software:

1.System software

2.Application software/PC software

3.Engg. &scientific software4.Real time software

5.Web based software

6.AI software

7.Embedded software

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System software : Managingandcontrollingoperationofcomputersystem. Itfrequentlyinteractwiththehardware.

Ex-OS ,assembler,compiler,linker,loaderetc.

Application software : usedforofficialandpersonaluseondailybasisandalsotosolveaparticularbusinessneed.Ex-MS word,MS office,mediaplayer,powerpointetc.

Engineering and scientific software : usedforscientificandengineeringactivities.

Ex-CAD, CAM , Mat Labetc.

Real time software : observes,analyzeandcontrolsrealworldeventsastheyoccur.

Ex- traffic lightcontrol.


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Web-based software : act asinterfacebetweenuserandinternet.Inotherwordsitisusedtodevelopwebbasedapplication.

Ex-HTML , ASP,webbrowseretc.AI software : usedwheretheproblemsolvingtechniqueis

nonalgorithmicinnature.

Ex-Robotics,gameplayingtechniqueetc.

Embedded software : itisverysmallandembeddedinasmallchiptoperformlimitedapplication.

Ex-automaticwashingmachine,s/win DVD playeretc.


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Legacy Software

Why must it change? softwaremustbeadapted tomeettheneeds

ofnewcomputingenvironmentsortechnology.

softwaremustbeenhanced toimplementnewbusinessrequirements.

softwaremustbeextended to make itinteroperable withothermoremodernsystems

ordatabases. softwaremustbere-architected tomakeit

viablewithinanetworkenvironment.


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Characteristics of software

1.Efficiency: thes/wmustusetheresourceproperly.

2.Maintainability: thes/wcanchangewithachangewithusers requirement.

3.On time: thes/wdevelopment mustbewithinthetimespecifiedbytheclient.

4.Within the budget: thedevelopment costofs/wshouldntexceedbudgetspecifiedbytheclient.

5.Functionality: itshouldmeetallthefunctionalityspecifiedbytherequirement.

6.Dependability: thes/wmustbesecuredandreliable.


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Characteristics of software

1. Softwareisdeveloped orengineered,itis

notmanufacturedintheclassicalsense.

2.softwaredoesnt wear out.


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Failure curve of hardware


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Wear vs. Deterioration


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SE is a layered technology


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Generic view of s/w Engg.:

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Emergence of SE:

1. Earlycomputer programming

2. Highlevellanguageprogramming

3. Controlflowbaseddesign

4. Structureorienteddesign

5. Datastructureorienteddesign

6. Datafloworienteddesign

7. Objectorienteddesign

8. Aspectorientationclient-serverdesign,embeddeds/wdesign.

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Early Computer Programming (50s) Every programmer developed

his own style of writing

programs: According to his intuition

(exploratory programming).(build & fix)

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What is Wrong with the Exploratory

Style?

Can successfully be used for very small

programs only.


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High-Level Language

Programming(Early 60s)

High-level languages such as

FORTRAN, ALGOL, and COBOL wereintroduced:

This reduced software developmentefforts greatly.

Software development style was still

exploratory. Typical program sizes were limited to a

few thousands of lines of source code.


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Control Flow-Based Design

(late60s) Size and complexity of programs

increased further:

Exploratory programming style

proved to be insufficient.

Programmers found:

Very difficult to write cost

effective and correct programs.

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Control Flow-Based Design (late60s)

Programmers found:

programs written by others very

difficult to understand and maintain.

To cope up with this problem,

experienced programmers advised:

``Pay particular attention to thedesign of the program's control

structure.'

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Control Flow-Based Design (late 60s)

A program's control structure

indicates:

The sequence in which the program'sinstructions are executed.

To help design programs having good

control structure: Flow charting technique was developed.


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Control Flow-Based Design (late 60s)

Using flow charting technique:

One can represent and design a program's

control structure. Usually one understands a program:

By mentally simulating the program's

execution sequence


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A program having a messy flow chart

representation:

Difficult to understand and debug


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It was found:

GO TO statements makes control

structure of a program messy. GO TO statements alter the flow of

control arbitrarily.

The need to restrict use of GO TOstatements was recognized.


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Many programmers had extensively used

assembly languages.

JUMP instructions are frequently usedfor program branching in assembly

languages.

Programmers considered use of GO TOstatements inevitable


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Control-flow Based Design (Late 60s)

At that time, Dijkstra published his

article:

Goto Statement Considered HarmfulComm. of ACM, 1969.

Many programmers were unhappy to read his

article.


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They published several counter articles:

Highlighting the advantages and

inevitability of GO TO statements


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But, soon it was conclusively proved:

Only three programming constructs are

sufficient to express any programminglogic:

sequence (e.g. a=0;b=5;)

selection (e.g. if(c=true) k=5 else m=5;) iteration (e.g. while(k>0) k=j-k;)

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Everyone accepted:

It is possible to solve any programming

problem without using GO TO statements. This formed the basis of Structured

Programming Methodology.


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Structured Programming

A program is called structured

When it uses only the following types of

constructs: sequence

selection

iteration


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Unstructured control flows are

avoided.

Consist of a neat set ofmodules.

Use single-entry, single-exit programconstructs.


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However, violations to this feature are

permitted:

Due to practical considerationssuch as:

Premature loop exit to support

exception handling.


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Structured programs are:

Easier to read and understand,

Easier to maintain, Require less effort and time for

development.


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Data Structure-Oriented Design

(Early70s)

Soon it was discovered:

It is important to pay more attention to the

design of data structures of a program Than to the design of its control structure.


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(Early70s)

Techniques which emphasize designing the

data structure:

Derive program structure from it:Are called data structure oriented Design

techniques.


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(Early70s)

Example of data structure oriented

design technique:

Jackson's Structured Programming(JSP)methodology

Developed by Michael Jackson in 1970s.


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Data Flow-Oriented Design (Late 70s)

Data flow-oriented techniques advocate:

The data items input to a system

must first be identified, Processing required on the data

items to produce the required

outputs should be determined.


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Data flow technique identifies:

Different processing stations (functions) in

a system.

The items (data) that flow between

processing stations.


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Data flow technique is a generic

technique:

Can be used to model the working ofany system.

not just software systems.

A major advantage of the data flowtechnique is its simplicity.


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Object-Oriented Design (80s)

Object-oriented technique:

An intuitively appealing design

approach: Natural objects (such as employees,

pay-roll-register, etc.) occurring in

a problem are first identified.


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Relationships among objects:

Such as composition, reference,

and inheritance are determined. Each object essentially acts as

A data hiding (or data abstraction)

entity.


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Object-Oriented Techniques have gained wide

acceptance:

Simplicity

Reuse possibilities

Lower development time and cost

More robust code

Easy maintenance


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Evolution of design techniques

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MODULE:I INTRODUCTION TO SOFTWARE

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COMPUTER SYSTEMS ENGINEERING

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Software Crisis

Software products:

Fail to meet user requirements.

Frequently crash. Expensive.

Difficult to alter, debug, and enhance.

Often delivered late. Use resources non-optimally

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Software Crisis (cont.)

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Factors Contributing to the Software

Crisis

Larger problems

Lack of adequate training in software

engineering

Increasing skill shortage

Low productivity improvements.

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Types of Software Projects

Software products

Outsourced projects Indian companies have focused on

outsourced projects.

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Reference

Fundamentals of Software Engineering,

Prentice-Hall of India, By R.Mall CHAPTER -1.

Software Engineering: A Practitioners

Approach,TMH, By R.S.Pressman,6th Edition,

CHAPTER-1.

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