SE Lecture 1.ppt

Chapter 1
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Software Engineering: A Practitioner’s Approach, 7/e
by Roger S. Pressman
Software Engineering 9/e
By Ian Sommerville
Software Engineering

What is Software?
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The product that software professionals build and then support
over the long term.
Software encompasses: (1) instructions (computer programs)
that when executed provide desired features, function, and
performance; (2) data structures that enable the programs to
adequately store and manipulate information and (3)
documentation that describes the operation and use of the
programs.

Software products
• Generic products
• Stand-alone systems that are marketed and sold to any customer who
wishes to buy them.
• Examples – PC software such as editing, graphics programs, project
management tools; CAD software; software for specific markets such as
appointments systems for dentists.
• Customized products
• Software that is commissioned by a specific customer to meet their
own needs.
• Examples – embedded control systems, air traffic control software,
traffic monitoring systems.
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Why Software is Important?
• The economies of ALL developed nations are dependent on
software.
• More and more systems are software controlled ( transportation,
medical, telecommunications, military, industrial, entertainment,)
• Software engineering is concerned with theories, methods and
tools for professional software development.
• Expenditure on software represents a
significant fraction of GNP in all developed countries.
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Software costs
• Software costs often dominate computer system costs. The
costs of software on a PC are often greater than the
hardware cost.
• Software costs more to maintain than it does to develop.
For systems with a long life, maintenance costs may be
several times development costs.
• Software engineering is concerned with cost-effective
software development.
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Features of Software?
• Its characteristics that make it different from other things human
being build.
Features of such logical system:
• Software is developed or engineered, it is not manufactured in
the classical sense which has quality problem.
• Software doesn't "wear out.” but it deteriorates (due to change).
Hardware has bathtub curve of failure rate ( high failure rate in the
beginning, then drop to steady state, then cumulative effects of dust, vibration, abuse
occurs).
• Although the industry is moving toward component-based
construction (e.g. standard screws and off-the-shelf integrated
circuits), most software continues to be custom-built. Modern
reusable components encapsulate data and processing into
software parts to be reused by different programs. E.g. graphical
user interface, window, pull-down menus in library etc. 6

Software Applications
• 1. System software: such as compilers, editors, file management utilities
• 2. Application software: stand-alone programs for specific needs.
• 3. Engineering/scientific software: Characterized by “ number
crunching”algorithms. such as automotive stress analysis, molecular biology,
orbital dynamics etc
• 4. Embedded software resides within a product or system. (key pad control of
a microwave oven, digital function of dashboard display in a car)
• 5. Product-line software focus on a limited marketplace to address mass
consumer market. (word processing, graphics, database management)
• 6. WebApps (Web applications) network centric software. As web 2.0
emerges, more sophisticated computing environments is supported
integrated with remote database and business applications.
• 7. AI software uses non-numerical algorithm to solve complex problem.
Robotics, expert system, pattern recognition game playing
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Software—New Categories
• Open world computing—pervasive, ubiquitous, distributed computing
due to wireless networking. How to allow mobile devices, personal
computer, enterprise system to communicate across vast network.
• Netsourcing—the Web as a computing engine. How to architect simple
and sophisticated applications to target end-users worldwide.
• Open source—”free” source code open to the computing community (a
blessing, but also a potential curse!)
• Also … (see Chapter 31)
• Data mining
• Grid computing
• Cognitive machines
• Software for nanotechnologies
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The IEEE definition:
Software Engineering: (1) The application of a systematic,
disciplined, quantifiable approach to the development,
operation, and maintenance of software; that is, the
application of engineering to software. (2) The study of
approaches as in (1).
The seminal definition:
[Software engineering is] the establishment and use of
sound engineering principles in order to obtain
economically software that is reliable and works
efficiently on real machines.
Software Engineering Definition
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Importance of Software Engineering
• More and more, individuals and society rely on advanced
software systems. We need to be able to produce reliable and
trustworthy systems economically and quickly.
• It is usually cheaper, in the long run, to use software
engineering methods and techniques for software systems
rather than just write the programs as if it was a personal
programming project. For most types of system, the majority of
costs are the costs of changing the software after it has gone
into use.
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FAQ aboutsoftwareengineering
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Question Answer
What is software? Computer programs, data structures and associated
documentation. Software products may be developed for
a particular customer or may be developed for a general
market.
What are the attributes of good software? Good software should deliver the required functionality
and performance to the user and should be
maintainable, dependable and usable.
What is software engineering? Software engineering is an engineering discipline that is
concerned with all aspects of software production.
What is the difference between software
engineering and computer science?
Computer science focuses on theory and fundamentals;
software engineering is concerned with the practicalities
of developing and delivering useful software.
What is the difference between software
engineering and system engineering?
System engineering is concerned with all aspects of
computer-based systems development including
hardware, software and process engineering. Software
engineering is part of this more general process.

Essential attributes of good software
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Product characteristic Description
Maintainability Software should be written in such a way so that it can evolve to
meet the changing needs of customers. This is a critical attribute
because software change is an inevitable requirement of a
changing business environment.
Dependability and
security
Software dependability includes a range of characteristics
including reliability, security and safety. Dependable software
should not cause physical or economic damage in the event of
system failure. Malicious users should not be able to access or
damage the system.
Efficiency Software should not make wasteful use of system resources such
as memory and processor cycles. Efficiency therefore includes
responsiveness, processing time, memory utilisation, etc.
Acceptability Software must be acceptable to the type of users for which it is
designed. This means that it must be understandable, usable and
compatible with other systems that they use.

A Layered Technology
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Software Engineering
a “quality” focus
process model
methods
tools
 Any engineering approach must rest on organizational commitment to quality which
fosters a continuous process improvement culture.
 Process layer as the foundation defines a framework with activities for effective
delivery of software engineering technology. Establish the context where products
(model, data, report, and forms) are produced, milestone are established, quality is
ensured and change is managed.
 Method provides technical how-to’s for building software. It encompasses many
tasks including communication, requirement analysis, design modeling, program
construction, testing and support.
 Tools provide automated or semi-automated support for the process and methods.

Software Process
• A process is a collection of activities, actions and tasks that are
performed when some work product is to be created. It is not
a rigid prescription for how to build computer software.
Rather, it is an adaptable approach that enables the people
doing the work to pick and choose the appropriate set of
work actions and tasks.
• Purpose of process is to deliver software in a timely manner
and with sufficient quality to satisfy those who have
sponsored its creation and those who will use it.
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Five Activities of a Generic
Process framework
• Communication: communicate with customer to understand objectives and
gather requirements
• Planning: creates a “map” defines the work by describing the tasks, risks and
resources, work products and work schedule.
• Modeling: Create a “sketch”, what it looks like architecturally, how the
constituent parts fit together and other characteristics.
• Construction: code generation and the testing.
• Deployment: Delivered to the customer who evaluates the products and
provides feedback based on the evaluation.
• These five framework activities can be used to all software development
regardless of the application domain, size of the project, complexity of the
efforts etc, though the details will be different in each case.
• For many software projects, these framework activities are applied iteratively
as a project progresses. Each iteration produces a software increment that
provides a subset of overall software features and functionality.
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Umbrella Activities
Complement the five process framework activities and help team manage and control
progress, quality, change, and risk.
• Software project tracking and control: assess progress against the plan and take
actions to maintain the schedule.
• Risk management: assesses risks that may affect the outcome and quality.
• Software quality assurance: defines and conduct activities to ensure quality.
• Technical reviews: assesses work products to uncover and remove errors before
going to the next activity.
• Measurement: define and collects process, project, and product measures to
ensure stakeholder’s needs are met.
• Software configuration management: manage the effects of change throughout
the software process.
• Reusability management: defines criteria for work product reuse and establishes
mechanism to achieve reusable components.
• Work product preparation and production: create work products such as models,
documents, logs, forms and lists.
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Adapting a Process Model
The process should be agile and adaptable to problems. Process adopted
for one project might be significantly different than a process adopted from
another project. (to the problem, the project, the team, organizational
culture). Among the differences are:
•the overall flow of activities, actions, and tasks and the interdependencies
among them
•the degree to which actions and tasks are defined within each framework
activity
•the degree to which work products are identified and required
•the manner which quality assurance activities are applied
•the manner in which project tracking and control activities are applied
•the overall degree of detail and rigor with which the process is described
•the degree to which the customer and other stakeholders are involved with
the project
•the level of autonomy given to the software team
•the degree to which team organization and roles are prescribed 18

Prescriptiveand Agile ProcessModels
•The prescriptive process models stress detailed definition,
identification, and application of process activates and tasks. Intent is
to improve system quality, make projects more manageable, make
delivery dates and costs more predictable, and guide teams of
software engineers as they perform the work required to build a
system.
•Unfortunately, there have been times when these objectives were
not achieved. If prescriptive models are applied dogmatically and
without adaptation, they can increase the level of bureaucracy.
•Agile process models emphasize project “agility” and follow a set
of principles that lead to a more informal approach to software
process. It emphasizes maneuverability and adaptability. It is
particularly useful when Web applications are engineered.
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The Essence of Practice
• How does the practice of software engineering fit in the process
activities mentioned above? Namely, communication, planning,
modeling, construction and deployment.
• George Polya outlines the essence of problem solving, suggests:
1. Understand the problem (communication and analysis).
2. Plan a solution (modeling and software design).
3. Carry out the plan (code generation).
4. Examine the result for accuracy (testing and quality assurance).
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Understand the Problem
• Who has a stake in the solution to the problem? That is,
who are the stakeholders?
• What are the unknowns? What data, functions, and
features are required to properly solve the problem?
• Can the problem be compartmentalized? Is it possible to
represent smaller problems that may be easier to
understand?
• Can the problem be represented graphically? Can an
analysis model be created?
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Plan the Solution
• Have you seen similar problems before? Are there patterns
that are recognizable in a potential solution? Is there existing
software that implements the data, functions, and features that
are required?
• Has a similar problem been solved? If so, are elements of the
solution reusable?
• Can sub-problems be defined? If so, are solutions readily
apparent for the sub-problems?
• Can you represent a solution in a manner that leads to
effective implementation? Can a design model be created?
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Carry Out the Plan
• Does the solutions conform to the plan? Is source code
traceable to the design model?
• Is each component part of the solution provably correct?
Has the design and code been reviewed, or better, have
correctness proofs been applied to algorithm?
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Additional software functionality
• Monitor the instruments, power and communication hardware and
report faults to the management system.
• Manage the system power, ensuring that batteries are charged
whenever the environmental conditions permit but also that
generators are shut down in potentially damaging weather
conditions, such as high wind.
• Support dynamic reconfiguration where parts of the software are
replaced with new versions and where backup instruments are
switched into the system in the event of system failure.
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SE Lecture 1.ppt