Software Engineering

E.M.G.YADAVA WOMEN’S COLLEGE, MADURAI-14
(An Autonomous Institution – Affiliated to Madurai Kamaraj University)
Re-accredited (3rd Cycle) with Grade A+ & CGPA 3.51 by NAAC
DEPARTMENT OF COMPUTER SCIENCE
V – Semester
SOFTWARE ENGINEERING
Roger S. Pressman
7th Edition
Mrs. V. JAYAVANI, M.S(IT&M).,
Assistant Professor of Computer Science

UNIT - I
OUTLINE
• TheNatureof Software
• WhatisSoftwareEngineering
• DefiningSoftware
• CharacteristicofSoftware
• SoftwareApplication Domains
• LegacySoftware

1.1 THE NAUTRE OF SOFTWARE
What is Engineering?
It is an application of science, tools and
methods to find cost effective solution to
problem.

What is Software Engineering?
Software engineering is defined as
systematic, disciplined and quantifiable approach
- for the development, operation and
maintenance of software

1.1.1 Defining SOFTWARE
Software is (1) instructions that when
executed provide desired features, function and
performance; (2) data structures that enable the
programs to adequately manipulate information, and
(3) descriptive information in both hard copy and
virtual forms that describes the operation and use of
the programs.

CHARACTERISTICS OF SOFTWARE
1. Software is developed or Engineered. It is not manufactured in the
classical sense.
 Although some similarities exist between software development and
hardware manufacturing, the two activities are fundamentally
different.
 In both activities, high quality is achieved through good design, but
the manufacturing phase for hardware can introduce quality problem
that are nonexistent for software.
 Both activities are dependent on people, but the relationship between
the people applied and work accomplished is entirely different.
 Both activities require the construction of s “Product”, but the
approaches are different.

CHARACTERISTICS OF SOFTWARE (Cont…)
2. Software doesn’t “Wear out”.
Figure: Failure curve for Hardware
Failure rate as a function of time for hardware. The relationship,
often called the “bathtub curve”, indicates the hardware exhibits
relatively high failure rates early in its life. The failure rate rises again as
hardware components suffer from the cumulative effects of dust,
vibration, abuse, temperature extremes, and many other environmental
maladies. State simply, the hardware begins to wear out.

Figure: Failure curves for software
When a hardware component wears out, it is replaced by a spare
part. There are no software spare parts. Every software failure indicates an
error in design or in the process through which design was translated into
machine executable code. Therefore, software maintenance involves
considerably more complexity

3. Although the industry is moving toward component-based
construction, most software continues to be custom built.
 As an engineering discipline evolves, a collection of standard
design components is created.
 Standard screws and off-the-shelf integrated circuits are only two of
thousands of standard components that are used by mechanical and
electrical engineers as they design new system.
 The reusable components have been created so that the engineer can
concentrate on the truly innovative elements of a design, that is, the
part of the design that represent something new.
 In the hardware world, component reuse is a natural part of the
engineering process.
 In the software world, it is something that has only begun to be
achieved on a broad scale.

1.1.2 Software Application Domains
 System Software
 Application Software
 Engineering / Scientific Software
 Embedded Software
 Product-line Software
 Web Application
 Artificial intelligence Software

Software Application Domains (Cont…)
System Software:
System software is a collection of programs written to
service other programs. It is characterized by heavy interaction with
computer hardware; heavy usage by multiple users; concurrent
operation that requires scheduling, resource sharing, and
sophisticated process management; complex data structures; and
multiple external interfaces.
Ex. Compilers, operating system, drivers etc.

Application Software :
Application software consists of standalone programs that solve a
specific business need. Application software is used to control the business
function in real-time.
Ex. E-mail applications, Spread-Sheets.
Engineering /Scientific Software:
Characterized by "number crunching" algorithms. Applications
range from astronomy to volcano logy, from automotive stress analysis to
space shuttle orbital dynamics, and from molecular biology to automated
manufacturing.
Ex. Computer Aided Design (CAD)

Embedded Software:
It resides in read-only memory and is used to control
products and systems. Embedded software can perform limited and
esoteric functions.
Ex. GPS Devices, Factory robots
Product-line Software:
Designed to provide a specific capability for use by many
different customers, product line software can focus on a limited and
esoteric marketplace.
Ex. Word processing, spreadsheet, CG, multimedia, etc.

Web Applications:
Web apps can be little more than a set of linked hypertext
files. It evolving into sophisticated computing environments that not
only provide standalone features, functions but also integrated with
corporate database and business applications.
Ex. Online auctions, Web mails…
Artificial Intelligence Software:
AI software makes use of non-numerical algorithms to solve
complex problems that are not amenable to computation or
straightforward analysis.
Ex. Robotics, expert system, game playing, etc.

Software New Categories
1. Open-world computing: The challenge for software engineers will be to
develop system and application software that will allow mobile devices,
personal computers and enterprise systems to communicate across vast
networks.
2. Netsourcing: The challenge for software engineers is to architect simple
(e.g: Financial planning) sophisticated applications that provide a benefit
to targeted end-user markets worldwide.
3. Open source: The challenge for software engineers is to build source
code that is self-descriptive, but more importantly, to develop techniques
that will enable both customers and developers to know what changes
have been made & how those changes manifest themselves within the

1.1.3 Legacy Software
Legacy Software…. Were developed decades ago and have been
continually modified to meet changes in business requirements and computing
platforms. The proliferation of such systems is causing headaches for large
organizations who find them costly to maintain and risky to evolve. Legacy
software often evolve for one or more of the following reasons:
 The software must be adapted to meet the needs of new computing
environments or technology.
 The software must be enhanced to implement new business requirements.
 The software must be extended to make it interoperable with other more
modern systems or databases.
 The software must be re-architected to make it viable within a network
environment.

Software Engineering

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