What is software engineering

Software engineering
 The economies of ALL developed nations are
dependent on software.
 More and more systems are software controlled
 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.

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.

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 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.
Introduction 4

Product specification
 Generic products
 The specification of what the software should do is owned by the
software developer and decisions on software change are made
by the developer.
 Customized products
 The specification of what the software should do is owned by the
customer for the software and they make decisions on software
changes that are required.
Introduction 5

Frequently asked questions about software
engineering
Introduction 6
Question Answer
What is software? Computer programs 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 are the fundamental software
engineering activities?
Software specification, software development, software
validation and software evolution.
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.

Frequently asked questions about software
engineering
Question Answer
What are the key challenges facing
software engineering?
Coping with increasing diversity, demands for reduced
delivery times and developing trustworthy software.
What are the costs of software
engineering?
Roughly 60% of software costs are development costs,
40% are testing costs. For custom software, evolution
costs often exceed development costs.
What are the best software engineering
techniques and methods?
While all software projects have to be professionally
managed and developed, different techniques are
appropriate for different types of system. For example,
games should always be developed using a series of
prototypes whereas safety critical control systems require
a complete and analyzable specification to be developed.
You can’t, therefore, say that one method is better than
another.
What differences has the web made to
software engineering?
The web has led to the availability of software services
and the possibility of developing highly distributed service-
based systems. Web-based systems development has led
to important advances in programming languages and
software reuse.
Introduction 7

Essential attributes of good software
Introduction 8
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.

Software engineering
 Software engineering is an engineering discipline that is
concerned with all aspects of software production from
the early stages of system specification through to
maintaining the system after it has gone into use.
 Engineering discipline
 Using appropriate theories and methods to solve problems
bearing in mind organizational and financial constraints.
 All aspects of software production
 Not just technical process of development. Also project
management and the development of tools, methods etc. to
support software production.
Introduction 9

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.
Introduction 10

Software process activities
 Software specification, where customers and engineers
define the software that is to be produced and the
constraints on its operation.
 Software development, where the software is designed
and programmed.
 Software validation, where the software is checked to
ensure that it is what the customer requires.
 Software evolution, where the software is modified to
reflect changing customer and market requirements.
Introduction 11

General issues that affect most software
 Heterogeneity
 Increasingly, systems are required to operate as distributed
systems across networks that include different types of computer
and mobile devices.
 Business and social change
 Business and society are changing incredibly quickly as
emerging economies develop and new technologies become
available. They need to be able to change their existing software
and to rapidly develop new software.
 Security and trust
 As software is intertwined with all aspects of our lives, it is
essential that we can trust that software.
Introduction 12

Software engineering diversity
 There are many different types of software system and
there is no universal set of software techniques that is
applicable to all of these.
 The software engineering methods and tools used
depend on the type of application being developed, the
requirements of the customer and the background of the
development team.
Introduction 13

Application types
 Stand-alone applications
 These are application systems that run on a local computer,
such as a PC. They include all necessary functionality and do
not need to be connected to a network.
 Interactive transaction-based applications
 Applications that execute on a remote computer and are
accessed by users from their own PCs or terminals. These
include web applications such as e-commerce applications.
 Embedded control systems
 These are software control systems that control and manage
hardware devices. Numerically, there are probably more
embedded systems than any other type of system.
Introduction 14

Application types
 Batch processing systems
 These are business systems that are designed to process data
in large batches. They process large numbers of individual
inputs to create corresponding outputs.
 Entertainment systems
 These are systems that are primarily for personal use and which
are intended to entertain the user.
 Systems for modeling and simulation
 These are systems that are developed by scientists and
engineers to model physical processes or situations, which
include many, separate, interacting objects.
Introduction 15

Application types
 Data collection systems
 These are systems that collect data from their environment using
a set of sensors and send that data to other systems for
processing.
 Systems of systems
 These are systems that are composed of a number of other
software systems.
Introduction 16

Software engineering fundamentals
 Some fundamental principles apply to all types of
software system, irrespective of the development
techniques used:
 Systems should be developed using a managed and understood
development process. Of course, different processes are used
for different types of software.
 Dependability and performance are important for all types of
system.
 Understanding and managing the software specification and
requirements (what the software should do) are important.
 Where appropriate, you should reuse software that has already
been developed rather than write new software.
Chapter 1 Introduction 17

Software engineering and the web
 The Web is now a platform for running application and
organizations are increasingly developing web-based
systems rather than local systems.
 Web services allow application functionality to be
accessed over the web.
 Cloud computing is an approach to the provision of
computer services where applications run remotely on
the ‘cloud’.
 Users do not buy software buy pay according to use.

Web software engineering
 Software reuse is the dominant approach for constructing
web-based systems.
 When building these systems, you think about how you can
assemble them from pre-existing software components and systems.
 Web-based systems should be developed and delivered
incrementally.
 It is now generally recognized that it is impractical to specify all the
requirements for such systems in advance.
 User interfaces are constrained by the capabilities of web
browsers.
 Technologies such as AJAX allow rich interfaces to be created within
a web browser but are still difficult to use. Web forms with local
scripting are more commonly used.

Web-based software engineering
 Web-based systems are complex distributed systems
but the fundamental principles of software engineering
discussed previously are as applicable to them as they
are to any other types of system.
 The fundamental ideas of software engineering,
discussed in the previous section, apply to web-based
software in the same way that they apply to other types
of software system.

What is software engineering

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