Software engn

8/10/2019 Software engn

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The course will enable the student to understandand appreciate:

1. The flow of events in software developmentefforts.

2. The role of a software engineer in system

development efforts.

Upon completion of this course, the student

should be able to specify, design, implement and

test a variety of software systems.


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Prescribed Text Book

1. Pressman, R.S., Software Engineering: A Practitioners

Approach, McGraw Hill Int. Student Ed., 6th Ed.,2005

2. Hoffer, Modern System Analysis and Design, Pearson

Education

Reference Books

KK Aggarwal, Yogesh Singh, Software Engineering, 2nd

Ed. New Age Publications, 2005

Jalote, P., An Integrated Approach to Software

Engineering, 3rd Ed., Narosa, 2005

Sommerville, I., Software Engineering, Pearson

Education, 7th Ed., 2005


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Lecture Break UpLecture No. Topic

01 Fundamentals

02-05 Software Process and Models

06-11 Software Requirements Engineering, Process Modeling, Data

Modeling ,Software Requirements Specification

12-16 Software Design, Process Oriented Design, User Interface Design

17-20 Software Testing ,Building Test Plan

21-23 Software Maintenance, Configuration Management

24 Quality Assurance Standards

25-26 Introduction to UML, Object Oriented Design

Tutorials Case Studies

Software Engineering Lab : Ms. Supriya

Software Modeling using Rational Rose

Lecture Break up


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Introduction

Getting started with software

engineering


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Objectives

To understand the notion of software engineering

and why it is important.

To set out the answers to key questions about

software engineering


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Historical Data

Data on 28,000 projects completed in 2000

This is the

SORRYstate

of SoftwareEngineering

Today!

Completed Late,

over budget,

and/or with

features missing53%

Cancelled

18%

Successful

29%


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Time (= Cost) of Postdelivery Maintenance

Development25%

Post-Delivery

Maintenance75%

Total Product CostsBreakout of

Development Costs

Integration

29%

Implementation/

Coding34%

Design

19%

Requirements &

Analysis18%


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Software costs often dominate system costs. The

costs of software on a PC are often greater than

the hardware cost

Software costs more to maintain than it does todevelop. For systems with a long life,

maintenance costs may be several times

development costs

Software engineering is concerned withcost-

effective software development

Why Software Engineering


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The Nature of SW...

SW is intangible

Hard to understand development effort

SW is easy to reproduce

Cost is in its development

in other engineering products, manufacturing is the costly stage

Quality problems are hard to notice

SW is easy to modify People make changes without fully understanding it

SW does not wear out It deteriorates by having its design changed:

erroneously, or

in ways that were not anticipated, thus making it complex


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The Nature of SW

ConclusionsMuch SW has poor design and is getting worse

Demand for SW is high and rising

We are in a perpetual SW crisis

We have to learn to engineer SW


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What is Software

Software is both: a Productand Vehicle for Delivering the

Product

As a product it delivers computing potential

embodied by computer hardware or morebroadly, a network of computers that areaccessible by local hardware

Whether software resides within a cellular phone

or operates inside a mainframe computer, it is aninformation transformerproducing, managing,acquiring, modifying displaying, or transmittinginformation that can be as simple as bit or as

complex as multimedia presentation


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What is Software

As a Vehiclesoftware acts as the basis for the

Control of the Computers (OS), the

Communication of Information(Networks)and

Creation and Controlof other Programs (software tools and environments)


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When it meets the needs of the people who use it

When it performs flawlessly over a long period of

time

When it is easy to modify and even easier to use

When a Software Succeeds


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Software engineering is the establishmentand use ofsound engineering principles in order to obtain

economically software that is reliable and works

efficientlyon real machines

Software engineering is the application of a

systematic, disciplined, quantifiable approach to

the development, operation and maintenance of

software, that is , the application of engineering tosoftware [IEEE90a]

Definition : Software Engineering


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Software Characteristics

Software is developed or

engineered, it is not

manufactured Software doesntwear out

Cost of Change at later stages is

high


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Software doesnt wear out

Failu

re

Ra

tes

Time

Infant

MortalityWear Out

Fig 1. Failure rate as a function of time for hardware


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Wear vs. Deterioration


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The Cost of Change


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Why does it take so long to get software

finished?

Why are development costs so high?

Why cantwe find all the errors before

we give the software to customers?

Why do we continue to have difficultyin measuring progress as software is

being developed

Concern about the Software[Crisis]


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Factors Contributing to the SW Crisis

Larger problems,

Lack of adequate training in SW

Engineering, Increasing skill shortage,

Low productivity improvements.


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Mastering complexity The efficiency with which software is

developed

Software engineering is a field in which

members of one culture create artifacts on

behalf of members of another culture

Visibility and continuity

Challenges

What are the key challenges facing


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What are the key challenges facingsoftware engineering?

Software Engineering faces three key challenges :

The Legacy Challenge:

The challenge is the challenge of maintainingand updating legacy software in such a way

that excessive cost are avoided and essential

business services continue to be delivered

K Ch ll


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Key Challenges

The Heterogeneity Challenge:

Increasingly, systems are required to operate

as distributed systems across networks that

include different types of computer and with

different kinds of support systems. The

heterogeneity challenge is the challenge of

developing techniques to build dependable

software which is flexible enough to copewiththis heterogeneity

K Ch ll


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Key Challenges

The Delivery Challenge:

Many traditional software engineering techniques

are time-consuming. The time they take is required

to achieve software quality. However, businesses

today must be responsive and change very rapidly.Their supporting software must change equally

rapidly. The delivery challenge is the challenge of

shortening delivery times of large and complex

systems without compromising system quality

D k


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That 80 percent of the engineering is consumed by 20percent of the requirements

80 percent of the software cost is consumed by 20 percent ofthe components

80 percent of the errors are caused by 20 percent of thecomponents

80 percent of the software scrap and rework is caused by 20percent of the changes

80 percent of the resource consumption (execution time, disk

space, memory etc.) is consumed by 20 percent of thecomponents

80 percent of the progress is made by 20 percent of thepeople

Do you know

SW M h (M P i )


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SW Myths (Management Perspectives)

As long as there are good standards and clear procedures

in my company, I shouldnt be too concerned.

But the proof of the puddingis in the eating;

not in the Recipe!


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As long as my SW engineers(!) have access to the fastest

and the most sophisticated computer environments and

state-of-the-art SW tools, I shouldnt be too concerned.

The environment isonly one of the several factors

that determine the qualityof the end SW product!


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When my schedule slips, what I have to do is to start a fire-fighting operation: add more SW specialists, those with higherskills and longer experience - they will bring the schedule backon the rails!

Unfortunately,SW business does not

entertain schedule compactionbeyond a limit!

SW M th (C t P ti )


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SW Myths (Customer Perspectives)

A general statement of objectives is sufficient to get

started with the development of SW. Missing/vague

requirements can easily be incorporated/detailed out as

they get concretized.

Application requirements can never be stable; SW can be

and has to be made flexibleenough to allow changes to be

incorporated as they happen.

h ( l i )


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SW Myths (Developer Perspectives)

Once the SW is demonstrated, the job is done.

Usually, the problems just begin!

SW M th (D l P ti )


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Until the SW is coded and is available for testing,

there is no way for assessing its quality.

Usually, there are too manytiny bugs inserted at every stagethat grow in size and complexity

as they progress thru further stages!




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The only deliverable for a SW development projectis the tested code.

The code is onlythe externally visible component

of the entire SW complement!


SW P d t


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SW Product

is a product designated for delivery to the user

sourcecodes

objectcodes

plans

reports

manuals

documents

test suitesprototypes

data

test results

What are the attributes of good


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software?

The software should deliver the required functionality and

performance to the user and should be maintainable, dependableand usable

Maintainability Software must evolve to meet changing needs

Dependability Software must be trustworthy

Efficiency Software should not make wasteful use of system resources

Usability Software must be usable by the users for which it was designed


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The Process

Th P


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Aprocess represents activities, tools,methods and practices that transform

inputs or raw materials, into outputs, or

finished products

The Process

Process Framework


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Process Framework

A process defines who is doingwhat, when and how to reach acertain goal

Jacobson, Booch, and Rumbaugh

S ft E i i A L d T h l


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Software Engineering : A Layered Technology

a quality focus

process

methods

tools

Quali ty FocusTotal Quality Management foster a continuous processimprovement culture, which leads to development ofincreasingly more mature approaches to SE

Software Engineering : A Layered Approach


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Software Engineering : A Layered Approach

Methods provide the technical how-tos for

building software. Methods encompasses a

broad array of tasks that include

requirements analysis, design, program

construction, testing and support

Toolsprovide automated or semi-automated

support for the process and the methods.

Process : Foundation for Software Engineering


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Process : Foundation for Software Engineering

SE Process is the glue that holds the technology

layers together and enables rational and timely

developmentof computer software

Process defines the framework that must beestablished for effective delivery of Software

Engineering Technology

The Software Process forms the basis for :


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The Software Process forms the basis for :

Management Controlof software projects

Establishes the Control in which technical

methods are applied

Work Products (models, documents, data,

reports, forms etc.) are Produced Milestonesare established

Qualityis ensured and

Changeis properly managed

Software Process


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Software Process

Product Engineering

Process

Process Management

Process

Development

Process

Project

Management

Process

Software

Configuration

management

Process

Software Process : Characteristics


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Predictability

Support Testability and Maintainability

Support Change

Early Defect Removal

Process Improvement and Feedback

Software Process


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Process FrameworkUmbrella Activities

Framework ActivityWork Tasks

Work Products

Milestones & deliverables

SQA points

Process Framework


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Process Framework establishes the foundation for acomplete software process by

identifying a small numberof framework activitiesthat are applicable to all software projectsregardless of their size or complexity

Process framework encompasses a set of umbrellaactivities that are applicable across the entiresoftware process

A number of tasks sets enable the frameworkactivities to be adapted to the characteristics ofthe software project and the requirements ofthe project team

Umbrella Activities


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Software project management Formal technical reviews

Software quality assurance

Software configuration management

Document preparation and production Reusability management

Measurement

Risk management

Finally, Umbrella activities overlay the process

model. Umbrella activities are independent ofany one framework activity and occur

throughout the process

The Process Model


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To solve actual problems in an industry

setting, a software engineer or a team ofengineers must incorporate a developmentstrategy that encompasses the process,methods and tools layers.

This strategy often referred as the ProcessModel

Software engn

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