Chapter 1. Introduction to Software Engineering.pptx

Why SoftwareEngineering?
• Change in nature & complexity of software
• Concept of one “guru” is over
• We all want improvement
Ready for change
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• Data on 28,000projectscompletedin 2000
This is the
SORRY state
of Software
Engineering
Today!
Completed
Late,over
budget,and/or
with features
missing – 49%
Cancelled–
23%
Successful–
28%
TheEvolvingRoleof SoftwareEngineering
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As per the IBM report, “31% of the project
get cancelled before they are completed, 53%
over- run their cost estimates by an average of
189% and for every 100 projects, there are 94
restarts”.
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• Unlike Hardware
– Moore’s law: processor
every two years
speed/memory capacity doubles
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Managers and Technical Persons are asked:
./ Why does it take so long to get the program finished?
./ Why are costs so high?
./ Why can not we find all errors before release?
./ Why do we have difficulty in measuring progress of software
development?
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FactorsContributingtotheSoftwareCrisis
• Larger problems,
• Lack of adequate training in software engineering,
• Increasing skill shortage,
• Low productivity improvements.
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SomeSoftwarefailures
Financial Software
Many companies have experienced failures in their
accounting system due to faults in the software itself. The
failures range from producing the wrong information to
the whole system crashing.
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SomeSoftwarefailures
Windows XP
oMicrosoft released Windows XP on October 25, 2001.
o On the same day company posted 18 MB of
compatibility patches on the website for bug fixes,
compatibility updates, and enhancements.
o Two patches fixed important security holes.
This is Software Engineering.
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The hardware cost continues to decline
drastically.
However, there are desperate cries for a
silver bullet something to make software
costs drop as rapidly as computer hardware
costs do.
But as we look to the horizon of a decade,
we see no silver bullet. There is no single
development, either in technology or in
management technique,
promises even one order
that by itself
of magnitude
improvement in productivity, in reliability
and in simplicity.
“
NoSilverBullet”
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The hard part of building software is the specification, design and
testing of this conceptual construct, not the labour of representing it
and testing the correctness of representation.
We still make syntax errors, to be sure, but they are trivial as compared
to the conceptual errors (logic errors) in most systems. That is why,
building software is always hard and there is inherently no silver
bullet.
 While there is no royal road, there is a path forward.
 Is reusability (and open source) the new silver bullet?
“
NoSilverBullet”
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“
NoSilverBullet”
The blame for software bugs belongs to:
• Software companies
• Software developers
• Legal system
• Universities
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What issoftware?
• Computer programs and associated
documentation
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Programs
Operating
Procedures
Documentation
Software=Program+Documentation+Operating Procedures
Components of software
What issoftware?
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Documentation
Manuals
Analysis
/Specification
Design
Implementation
Testing
Formal Specification
Context-Diagram
Data Flow Diagrams
Flow Charts
Entity-Relationship
Diagram
Source Code Listings
Cross-Reference
Listing
Test Data
Test Results
Documentationconsistsof differenttypes of manualsare
List of documentation manuals
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Operating
Procedures
Installation Guide
Operational
Manuals
System
Administration Guide
List of operating procedure manuals.
User
Manuals
System Overview
Beginner’s Guide
Tutorial
Reference Guide
Documentationconsistsof differenttypes of manualsare
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• Software products may be developed for a particular
customer or may be developed for a general market
• Software products may be
 Generic- developed to be sold to a range of different
customers
 Bespoke (custom) - developed for a single customer
according to their specification
SoftwareProduct
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Software product is a product designated for
delivery to the user
Objects
Codes
SoftwareProduct
Source
Codes
Reports Documents
Plans
Test
Suites Test
results
Prototypes
Data
Manuals
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What issoftwareengineering?
Software engineering is an engineering discipline which
is concerned with all aspects of software production
Software engineers should:
 adopt a systematic and organised approach to
their work
 use appropriate tools and techniques depending on
• the problem to be solved,
• the development constraints and
 use the resources available
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At the first conference on software engineering in 1968, Fritz Bauer
defined software engineering as “The establishment and use of
sound engineering principles in order to obtain economically
developed software that is reliable and works efficiently on real
machines”.
Stephen Schach defined the same as “A discipline whose aim is the
production of quality software, software that is delivered on time,
within budget, and that satisfies its requirements”.
Both the definitions are popular and acceptable to majority.
However, due to increase in cost of maintaining software, objective
is now shifting to produce quality software that is maintainable,
delivered on time, within budget, and also satisfies its requirements.
What issoftwareengineering?
4/3/2024

SoftwareProcess
The software process is the way in which we produce
software.
Why is it difficult to improve software process ?
• Not enough time
• Lack of knowledge
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Learning curve
Do not quit here!
Improved future state
Process improvement
begins
Initial state
state
Productivity
Time
• Wrong motivations
• Insufficient commitment
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SoftwareProcess

SoftwareCharacteristics:
arout
hase
./Software does not wear out.
Burn-in
phase We
Useful life
phase
p
Failure
Intensity
Time
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./ Software is not manufactured
./ Reusability of components
./ Software is flexible
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Comparison of constructing a bridge vs writing a program.
Sr.
No
Constructing a bridge Writing a program
1. The problem is well understood Only some parts of the problem are
understood, others are not
2. There are many existing bridges Every program is different and designed for
special applications.
3. The requirement for a bridge typically do
not change much during construction
Requirements typically change during all
phases of development.
4. The strength and stability of a bridge can be
calculated with reasonable precision
Not possible to calculate correctness of a
program with existing methods.
5. When a bridge collapses, there is a
detailed investigation and report
When a program fails, the reasons are often
unavailable or even deliberately concealed.
6. Engineers have been constructing bridges
for thousands of years
Developers have been writing programs
for 50 years or so.
7. Materials (wood, stone,iron, steel) and
techniques (making joints in wood, carving
stone, casting iron) change slowly.
Hardware and software changes rapidly.

System
Software
Real
Time
Software
Embedded
Software
Business
Software
Engineering
and Scientific
Software
Web based
Software
Artificial
Intelligence
Software
Personal
Computer
Software
TheChanging Natureof Software
4/3/2024

TheChanging Natureof Software
Trend has emerged to provide source code to the customer
and organizations.
Software where source codes are available are known as open
source software.
Examples
Open source software: LINUX, MySQL, PHP, Open office, Apache
webserver etc.
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Management may be confident about good
standards and clear procedures of the company.
But the taste of any food item
is in the eating;
not in the Recipe !
SoftwareMyths (Management Perspectives)
4/3/2024

Company has latest computers and state-of-
the-art software tools, so we shouldn’t worry
about the quality of the product.
The infrastructure is
only one of the several factors
that determine the quality
of the product!
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Addition of more software specialists, those
with higher skills and longer experience may
bring the schedule back on the track!
Unfortunately,
that may further delay the schedule!
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Software is easy to change
The reality is totally different.
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Computers provide greater reliability
the devices they replace
than
This is not always true.
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A general statement of objectives is sufficient to get started with
the development of software. Missing/vague requirements can
easily be incorporated/detailed out as they get concretized.
If we do so, we are heading
towards a disaster.
Software Myths (Customer Perspectives)
4/3/2024

Software with more features is better software
Software can work right the first time
Both are only myths!
Software Myths (Customer Perspectives)
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Once the software is demonstrated, the job is done.
Usually, the problems just begin!
SoftwareMyths (DeveloperPerspectives)
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Software quality can not be assessed before
testing.
However, quality assessment techniques
should be used through out the
software development life cycle.
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The only deliverable for a software
development project is the tested code.
Tested code is only one of the deliverable!
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Aim is to develop working programs
Those days are over. Now objective is to
develop good quality maintainable
programs!
4/3/2024

Thank YOU
On the next class come with
your formed group and title
4/3/2024

Chapter 1. Introduction to Software Engineering.pptx

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Chapter 1. Introduction to Software Engineering.pptx