Chapter 1- Introduction

Chapter 1 Introduction 1
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.

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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
costs.

 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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 Software project failure

 Increasing system complexity

 As new software engineering techniques help us to build larger, more
complex systems, the demands change. Systems have to be built and
delivered more quickly; larger, even more complex systems are
required; systems have to have new capabilities that were previously
thought to be impossible.
 Failure to use software engineering methods
 It is fairly easy to write computer programs without using software
engineering methods and techniques. Many companies have drifted into
software development as their products and services have evolved.
They do not use software engineering methods in their everyday work.
Consequently, their software is often more expensive and less reliable
than it should be.

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Frequently asked questions about software
engineering

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 Software specification, software development, software
engineering activities? validation and software evolution.
What is the difference between software Computer science focuses on theory and fundamentals; software
engineering and computer science? engineering is concerned with the practicalities of developing
and delivering useful software.
What is the difference between software System engineering is concerned with all aspects of computer-
engineering and system engineering? based systems development including hardware, software and
process engineering. Software engineering is part of this more
general process.

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Frequently asked questions about software
engineering

Question Answer

What are the key challenges facing Coping with increasing diversity, demands for reduced delivery times
software engineering? and developing trustworthy software.

What are the costs of software Roughly 60% of software costs are development costs, 40% are
engineering? testing costs. For custom software, evolution costs often exceed
development costs.

What are the best software engineering While all software projects have to be professionally managed and
techniques and methods? 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 The web has led to the availability of software services and the
software engineering? possibility of developing highly distributed service-based systems.
Web-based systems development has led to important advances in
programming languages and software reuse.

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 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.

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 Essential attributes of good software

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.

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 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.

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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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 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.

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 Application types

 Stand-alone applications
 These are application systems that run on a local computer, such as a
PC.
 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.

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 Application types (continued)

 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 modelling and simulation
 These are systems that are developed by scientists and engineers to
model physical processes or situations, which include many, separate,
interacting objects.

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 Application types (continued)

 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.

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 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.
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Internet and web-based software engineering

 The Web is now a platform for running application and

organizations are increasingly developing web-based systems
rather than local systems.

 Cloud computing is an approach to the provision of computer

services where applications run remotely on the ‘cloud’.
 Users do not buy software but pay according to use.

 Web-based systems are complex distributed systems but the

fundamental principles of software engineering are as
applicable to them as they are to any other types of system.
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 Web-based software engineering

 Software reuse
 When building these systems, you think about how you can assemble
them from pre-existing software components and systems.
 Incremental and agile development
 Web-based systems should be developed and delivered incrementally.
 Service-oriented systems
 Software may be implemented using service-oriented software
engineering, where the software components are stand-alone web
services.
 Rich interfaces
 Interface development technologies such as HTML5 have emerged that
support the creation of rich interfaces within a web browser.
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 Software engineering ethics

 Software engineering involves wider responsibilities than simply

the application of technical skills.

 Software engineers must behave in an honest and ethically

responsible way if they are to be respected as professionals.

 Ethical behaviour is more than simply upholding the law but

involves following a set of principles that are morally correct.

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 Issues of professional responsibility

 Confidentiality
 Engineers should normally respect the confidentiality of their employers
or clients irrespective of whether or not a formal confidentiality
agreement has been signed.
 Competence
 Engineers should not misrepresent their level of competence. They
should not knowingly accept work which is outwith their competence.
 Intellectual property rights
 Engineers should be aware of local laws governing the use of intellectual
property such as patents, copyright, etc.
 Computer misuse
 Software engineers should not use their technical skills to misuse other
people’s computers.
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 Case studies

 A personal insulin pump

 An embedded system in an insulin pump used by diabetics to maintain
blood glucose control.

 A mental health case patient management system

 Mentcare. A system used to maintain records of people receiving care for
mental health problems.

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 Insulin pump control system

 Collects data from a blood sugar sensor and calculates the

amount of insulin required to be injected.

 Calculation based on the rate of change of blood sugar levels.

 Sends signals to a micro-pump to deliver the correct dose of

insulin.

 Safety-critical system as low blood sugars can lead to brain

malfunctioning, coma and death; high-blood sugar levels have
long-term consequences such as eye and kidney damage.
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Insulin pump hardware architecture

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Activity model of the insulin pump

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 Essential high-level requirements

 The system shall be available to deliver insulin when required.

 The system shall perform reliably and deliver the correct

amount of insulin to counteract the current level of blood sugar.

 The system must therefore be designed and implemented to

ensure that the system always meets these requirements.

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 Mentcare: A patient information system for
mental health care

 A patient information system to support mental health care is a

medical information system that maintains information about
patients suffering from mental health problems and the
treatments that they have received.
 Most mental health patients do not require dedicated hospital
treatment but need to attend specialist clinics regularly where
they can meet a doctor who has detailed knowledge of their
problems.
 To make it easier for patients to attend, these clinics are not just
run in hospitals. They may also be held in local medical
practices or community centres.

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 Mentcare

 Mentcare is an information system that is intended for use in

clinics.

 It makes use of a centralized database of patient information

but has also been designed to run on a PC, so that it may be
accessed and used from sites that do not have secure network
connectivity.

 When the local systems have secure network access, they use
patient information in the database but they can download and
use local copies of patient records when they are
disconnected.
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The organization of the Mentcare system

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 Key features of the Mentcare system

 Individual care management

 Clinicians can create records for patients, edit the information in the
system, view patient history, etc. The system supports data summaries
so that doctors can quickly learn about the key problems and treatments
that have been prescribed.
 Patient monitoring
 The system monitors the records of patients that are involved in
treatment and issues warnings if possible problems are detected.
 Administrative reporting
 The system generates monthly management reports showing the
number of patients treated at each clinic, the number of patients who
have entered and left the care system, number of patients sectioned,
the drugs prescribed and their costs, etc.
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 Mentcare system concerns

 Privacy
 It is essential that patient information is confidential and is never
disclosed to anyone apart from authorised medical staff and the patient
themselves.
 Safety
 Some mental illnesses cause patients to become suicidal or a danger to
other people. Wherever possible, the system should warn medical staff
about potentially suicidal or dangerous patients.
 The system must be available when needed otherwise safety may be
compromised and it may be impossible to prescribe the correct
medication to patients.

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