short question (200words)
No need to cite, but you must read the material carefully and find answers from the material. Finish it in 12 hours
Q1: What is the difference between the terms user interface and human-computer interaction? Contrast the two terms, do not just define them.
Q2: What is the importance of a good user interface design? What are some of the potential consequences of poor user interface design? List at least 2 points for each 1
Introduction
1 Why the User Interface Matters
Humancomputer interaction (HCI) is the study of how humans interact with
computer systems. Many disciplines contribute to HCI, including computer science,
psychology, ergonomics, engineering, and graphic design. HCI is a broad term
that covers all aspects of the way in which people interact with computers. In
their daily lives, people are coming into contact with an increasing number of
computer-based technologies. Some of these computer systems, such as personal
computers, we use directly. We come into contact with other systems less directly
for example, we have all seen cashiers use laser scanners and digital cash registers
when we shop. And, as we are all too aware, some systems are easier to use than
others.
When users interact with a computer system, they do so via a user interface (UI).
This book explores how to design good user interfaces interfaces that are easy to
use and easy to understand, that meet the needs of the intended users, and that
support users in the tasks they wish to undertake. In this part of the book, we intro-
duce you to user interface design and evaluation. In particular, we explain why good
user interface design is important and highlight the consequences of poor or bad
user interface design. More important, we will get you to start thinking about users
and why and how to involve them in the design and evaluation of the user
interface.
2 Computers Are Ubiquitous
Technology has advanced so much that computer systems are used on an everyday
basis by almost everyone. A computer system (or an interactive computer system
or just a system) is the combination of hardware and software components that
receive input from, and communicate output to, a user in order to support his or her
performance of a task (see Figure 1.1). Computer systems may be used directly, as in
the case of personal computers (PCs) in use at work or at home. Often, though, we
use embedded computer systems where the technology is invisible to us. For
3
Part 1
example, computer-based mi-
crochip technology can be
found embedded in personal
goods such as digital watches
and mobile phones, in do-
mestic appliances such as
microwave ovens, washing
machines, and video re-
corders, and in the instru-
ment panels of cars. Again,
but less directly, computers
are used when we shop;
many stores use laser scan-
ners that swipe the bar
codes on goods to record
both the goods we purchase
and total the amounts we
spend. Behind the scenes,
the scanning of goods assists
with automated stock control
and stock reordering. When we take money from our bank accounts using an auto-
mated teller machine (ATM) or when we use ATM debit cards to buy goods elec-
tronically, our bank details are accessed via the banks computer system. The list of
everyday ways in which we use computer-based systems seems endless.
Whether we are aware of it or not, computers pervade our life. Computer applica-
tions are used either by us, or for us, in some way almost every day. The user inter-
face (or just interface) is that part of the computer system with which a user interacts
in order to undertake his or her tasks and achieve his or her goals.
The user interface and the ways of interacting with computer-based systems are dif-
ferent for each system. For example, digital watches generally have buttons that users
press to set the time or use the stopwatch facility. Microwave ovens might have dials
to turn or a digital display and a touchpad of buttons to set the cooking time. PCs
have a screen, a keyboard, and a mouse (or sometimes a trackball or a joystick) that
enable interaction to take place. So each user interface is different. Depending on
the design of the interface, each of these systems will either be usable that is, easy
to learn and easy to use or problematic for users.
Earlier we described a computer system as the combination of hardware and soft-
ware components that receive input from, and communicate output to, a user to
support his or her performance of a task. Although the user interface is simply the
part of the computer system that enables interaction and serves as a bridge between
users and the system, to users the interface often is the system (Constantine and
Lockwood, 1999). The users view of a computer system is often limited to and based
solely on his or her experience of the user interface (see Figure 1.2).
CHAPTER 1 | Introduction
4
Part 1
Figure 1.1 The interface is the part of the computer system
with which the user interacts in order to use the system and
achieve his or her goal.
For example, when you use the controls on the panel of a washing machine, the con-
trols form the interface between you and the machine you are not concerned with
the underlying technology or the software of the washing machine itself. What is
important to you is that the controls and their settings are intuitive and easy to under-
stand and use so that you will achieve your goal of laundering clothes. Similarly, when
you surf the Internet, the pages of a web site displayed on your PCs monitor form
the interface between you and the site. The web page UI may contain controls like
scroll bars, clickable hot spots, or links in the form of text or images. These items are
all part of the interface.
3 The Importance of Good User Interface Design
Good user interface design is important because, as we have discussed, computer
use permeates everyday life. Early computer systems were expensive and were devel-
oped mainly for particular tasks, like advanced number-crunching; as such, these
systems were employed only by specialist computer users. Often the systems had
command-line interfaces, with obscure commands known only by these specialist
users. Thus, the user had to adapt to the system, and learning how to use the system
required much effort.
Computing systems, however, are no longer the province of the specialist user. As the
price of PCs and computer-based technologies has fallen, the ownership of these
types of goods by nonspecialists has widened. In August 2000, 51% of households in
the United States had access to one or more home computers, and 42% of house-
holds had access to the Internet (U.S. Census Bureau, 2001). In 2002, 54% of house-
holds in the United Kingdom had access to some form of home computer, and 44%
had access to the Internet (National Statistics, 2004). Therefore, the need for the
design and development of user interfaces that support the tasks people want to do
and that can be used easily by a variety of people with varying abilities has become
3. The Importance of Good User Interface Design
5
Part 1
User
interface
User input
System output
Underlying
hardware, software,
interaction devices
Figure 1.2 To the user, the interface is the computer system. (From Constantine and Lockwood,
1999.)
You will learn
more about
command-line
interfaces and
other interaction
styles in
Chapter 11.
The design of
controls, and
the selection of
interaction
devices for
input and
output, will be
discussed
further in
Chapters 12
through 14.
an important issue. Users are more comfortable with computer systems that are easy
to use, easy to understand, and enable them to attain their goals with minimum
frustration.
One way of demonstrating the importance of good user interface design is by
showing tangible benefits that can be discussed in cash terms. For businesses, good
user interfaces can lead to benefits such as higher staff productivity, lower staff
turnover, higher staff morale, and higher job satisfaction. Economically, these bene-
fits should translate into lower operating costs. In addition, computer systems that
are easy to use and easy to understand require less training, again saving employers
money. Bad user interfaces, on the other hand, may result in stress and unhappiness
among staff, leading to high staff turnover, reduced productivity, and, consequently,
financial losses for the business. As you will see later, it is easy to give examples of
the effects of bad design, but showing the financial benefits of good user interface
design can be more difficult. Invariably, many factors are involved and this makes it
difficult to attribute success directly to good user interface design.
3.1 What Is a Good User Interface Design?
A good user interface design encourages an easy, natural, and engaging interaction
between a user and a system, and it allows users to carry out their required tasks.
With a good user interface, the user can forget that he or she is using a computer and
get on with what he or she wants to do. Just as knowledge of the transmission mech-
anism of a car is of little concern to most motorists, knowledge of the internal work-
ings of a computer system should be of little consequence to its users.
Although we have used the adjectives good, poor, and bad to describe user
interfaces, it is worth noting that each of these terms is subjective: they have differ-
ent meanings for different people and their use to rate various aspects of a user inter-
face will vary. You may have used the terms good or bad to describe, for example,
the colors used in an interface, the pictures on the icons, or how attractive or eye-
catching the interface was. These attributes describe the overall look or aesthetics of
the UI. Nevertheless, they are only a part of our focus in this book. Our real concern
is whether a user interface is good, bad, or poor in relation to its usability.
What Is Usability?
Usability is defined in Part 11 of the ISO 9241 standard (BSI, 1998) as the extent
to which a product can be used by specified users to achieve specified goals with
effectiveness, efficiency and satisfaction in a specified context of use. Effectiveness
is the accuracy and completeness with which specified users can achieve specified
goals in particular environments. Efficiency is defined as the resources expended in
relation to the accuracy and completeness of the goals achieved. Satisfaction is the
comfort and acceptability of the work system to its users and other people affected
by its use.
Note two key aspects of this definition of usability. First, to be usable an interface
should be perceived as being usable by the specified users users for whom the
system has been designed and developed. Next, the scope of focus for the design of
CHAPTER 1 | Introduction
6
Part 1
We discuss
some alternative
definitions of
usability in
Chapter 6.
the interface is extended by looking beyond the users immediate work environment
and looking at the wider context or situation within which the system is expected to
operate (i.e., the domain, tasks, and the environment that make up an organization).
Thus, usability is concerned with the extent to which users of an application are able
to work effectively, efficiently, and with satisfaction in their particular contexts.
A computer system that is usable in one context may be unusable in another. As a
user interface designer, it is important to consider the context in which the system
will be used. A UI that users find pleasurable is likely to be more acceptable than one
that annoys them. Users are more likely to use a computer system that they enjoy
than one that irritates them. Contented users are likely to be more productive, so
usability is clearly related to user satisfaction (Constantine and Lockwood, 1999).
3.2 The Problems of Poor or Bad User Interfaces
User Frustration and Dissatisfaction
Problems for users and the public in general arise as a result of poorly designed user
interfaces. The term computer rage was coined in 1999 following a Market &
Opinion Research International (MORI) poll conducted on behalf of Compaq Com-
puter Limited, UK and Ireland. The study, Rage against the Machine (Compaq, 1999),
(www.mori.com /polls /2002/bthomecomputing.shtml) found that, for one reason or
another, stress and frustration levels with workplace technology are rising. Workers,
it reports, have started to become both verbally and physically abusive toward the
information technology (IT) in use (see Figure 1.3 and Box 1.1). Concerning mone-
tary matters, the study indicates that
[t]he cost to business of this increase in stress levels of employees is not only based
on sick days or under-performance, but also the working time lost through waiting
for IT problems to be solved. Confederation of British Industry (CBI) statistics cur-
rently evaluate this at a staggering 25,000 ($40,000) per person in lost business
each year (based on one hour
a day being spent sorting out
IT problems). (p. 4)
In October 2002, research for
British Telecom (BT) Home
Computing, (www.mori.com /
polls /2002 /bthome-topline.
shtml) again conducted by
MORI, found that 70% of per-
sonal computer users suffered
from PC rage that is, the
users surveyed admitted to
shouting, swearing, or being
violent to their computers
when problems like crashing
or virus infections arise.
You will learn
more about
domains, tasks,
and environ-
ments in
Chapter 4.
3. The Importance of Good User Interface Design
7
Part 1
Figure 1.3 Computer rage: Workers have started to
become physically (and verbally) abusive toward IT.
CHAPTER 1 | Introduction
8
Part 1
Box 1.1 Man Shoots Laptop
A 48-year-old man, George Doughty, was allegedly so frustrated by his laptop
crashing that he took a handgun and shot it four times. According to police he
apparently hung the destroyed laptop on a wall as if it were a hunting trophy.
Lafayette police officer Rick Bashor told local newspapers, Its sort of funny,
because everybody always threatens their computers, [but] its the first time
someone shot a computer because he was upset with it. The man admitted to
police that he should not have shot his laptop, but that it seemed appropriate
to at the time.
From http://news.bbc.co.uk/1/hi/world/americas/2826587.stm,
reported March 6, 2003, downloaded June 1, 2004
Box 1.2 Survey Highlights Computer Rage
One in five Scots suffers from Internet rage and some feel like hurling their
computers through a window, according to a survey undertaken in February
2004. Around 1000 Scots were asked to tick a box with several options about
their pet hates in everyday life for the survey this month. Some 45% of those
polled blamed sluggish Internet connections for making their blood boil. This
was more than twice the number of people (20%) who said watching their
favourite soccer team get beaten drove them mad. . . . One in 10 surfers con-
fessed they sometimes felt like punching their keyboard, whacking the monitor
with a hammer and even throwing their PCs out the window. A third of people
quizzed said they had to walk away to cool down. Additionally, one fifth of Scots
feel that slow Internet connections at work make them lose up to an hour a day.
From Jude Sheerin, PA News, as reported at news.scotland.com,
http://news.scotsman.com/latest.cfm?id=2522311, February 12, 2004.
Despite more than two decades of HCI research, it remains an unfortunate fact that
many computer systems do not do what users want them to do. Users often describe
their difficulties in system use as computer problems, which is nonspecific as to the
source of the problems. There could be several explanations. For example, the prob-
lems could be related to buggy software or to the use of older, less efficient hardware
or technology that slows the processing of information. Or maybe there was no clear
understanding about the work environments in which the new computer systems
were expected to operate. Box 1.3 looks at problems that occurred when the UK
Passport Agency introduced a new computer system.
Equally, a poorly designed user interface could have contributed to the problems.
While there is no direct evidence in any of the news reports to suggest that poor user
interface design was to blame, it is likely that user interface problems contributed to
the difficulties that users had with these systems.
EXERCISE 1.1 (Allow 10 minutes)
Think for a moment about the situation outlined in Box 1.3. Suggest what the
consequences of the Passport Agencys computer problems may have been for
the following groups of people:
The general public
The workers at the Passport Agency
DISCUSSION
The consequences to the general public were enormous. People had great diffi-
culty getting their passports in time for their vacations. People waiting for pass-
ports may have suffered from stress and anxiety related to the possibility that
they may not be able to go away. Some may have lost money as a result of being
unable to travel. Business travelers would have been affected too. Both groups
probably felt anger and frustration with what they would have perceived as com-
puters being in control and staffed by unorganized, incompetent government
administrators. Furthermore, many people had to take time off work to line up
for hours at passport offices. The passport agency workers, too, suffered conse-
quences. They would have been under great stress to meet the demands of the
public, and they would have felt anger and frustration because the system did
not enable them to do their jobs of processing passport applications and issuing
passports.
Loss of Productivity, Efficiency, and Money
Computer systems with poor user interfaces can have a financial cost. Take the crisis
at the Passport Agency. It was reported that the cost of this fiasco was $20 million
3. The Importance of Good User Interface Design
9
Part 1
Box 1.3 Passport Agency Delays
In May 1999 the UK Passport Agency hit the headlines as the waiting time for
a passport applied for by post lengthened from a target time of two weeks to
between seven and ten weeks. While this increase in waiting times was partly
due to a larger than expected increase in passport applications (because of a
new requirement for children to have their own passports), a second reason
cited was computer problems caused by the introduction of new computer
systems at two of the Passport Agencys offices. Applicants anxious to ensure
that they would have their passports in time to holiday abroad queued by the
hundreds in Glasgow, Liverpool, and London.
Drawn from the BBC News web site,
June 15, June 24, June 28, and June 29, 1999.
(12.6 million), which included nine million dollars (six million pounds) on staff
overtime and at least $242,000 (161,000) in compensation to the hundreds of people
who missed their vacations as a result of not receiving their passports on time. The
Passport Agency also spent $24,000 (16,000) on umbrellas for people who had to
wait outside of passport offices in the rain to get their passports over the counter.
Subsequently the price of a passport was increased. The supplier of the computer
system had agreed to pay $3.7 million (2.45 million) of the costs, leaving the remain-
der to be paid by the taxpayer. In these days of payment for productivity and effi-
ciency, wages may have been lost if agency workers earnings were linked to a level
of productivity they were unable to meet because the computer system was unfit for
its purpose.
3.3 Safety and the User Interface
So far we have considered the problems of poor user interfaces in terms of user frus-
tration and dissatisfaction, and the loss of productivity and efficiency to business.
There is another important aspect to consider: the issue of safety, both for computer
systems users and the general public.
Systems in which human or environmental safety is of paramount concern are
referred to as safety-critical systems. These systems include aircraft, aircraft flight
decks, air traffic control consoles, nuclear power plants, control systems, and medical
devices. The Three Mile Island nuclear power plant disaster (see Figure 1.4 and Box
1.4) illustrated that safety can be severely compromised by poor user interface
design, with potentially serious consequences.
CHAPTER 1 | Introduction
10
Part 1
Box 1.4 The Three Mile Island Nuclear Power Plant Disaster
One of the most discussed issues during the early 1980s was the Three Mile
Island nuclear power plant disaster. The incident nearly resulted in a meltdown
of the nuclear reactor. The cause of the incident was never conclusively deter-
mined, but experts, official bodies, and the media all blamed a combination of
operator error and bad interface design. In particular, much media attention
and several official reports focused on the design of the control panels in the
process plant. The incident could have been prevented if the control panels
had been designed to provide the operators with the necessary information to
enable them to perform their tasks efficiently and correctly. The following are
just some of the interface problems that were identified:
A light indicated that a valve had been closed when in fact it had not.
The light indicator was obscured by a caution tag attached to another valve
controller.
3. The Importance of Good User Interface Design
11
Part 1
Figure 1.4 The Three Mile Island nuclear power plant.
The control room alarm system provided audible and visual indication for
more than 1500 alarm conditions. Evidently this number of alarms was
intended to facilitate control of the entire plant during normal operating
conditions. However, the layout and grouping of controls on the control
panel had not been well thought out and so enhanced, rather than mini-
mized, operator error (Brookes, 1982; cited in Leveson, 1995).
A single acknowledge button silenced all the alarms at the same time, but
it was not used because the operators knew they would lose information if
they silenced some of the alarms. There was simply no way for the operators
to cancel the less important signals so that they could attend to the impor-
tant ones.
The root of the problem, therefore, seemed to be that the control panels did
not support the task of serious error and incident recovery. The control panels
misinformed the operators. They did not indicate to the operators the true state
of affairs in the reactor plant, and they did not provide the necessary informa-
tion in a form that the operators could understand and use to rectify the
situation.
3.4 Elections and the User Interface
In November 2000, the topic of user interface design suddenly became international
news when the outcome of the U.S. presidential election hung on the results of one
county in Florida. In this elec-
tion, an apparently minor
aspect of equipment design
turned out to have major con-
sequences. Many voters in
Palm Beach County felt that
their vote went to the wrong
person (see Box 1.5).
State law in Florida limited the
time in the voting booth
(Figure 1.5) to five minutes.
The design of the ballot (Figure
1.6) was considered by some to
be difficult to understand.
After the election, some voters
said that they wanted to vote
CHAPTER 1 | Introduction
12
Part 1
Figure 1.5 The type of ballot booth used in Palm Beach
County. Steve Krug 2004, used with permission.
Figure 1.6 The problematic page of the ballot in the booth. Steve Krug 2004, used with permission.
for Gore (which required them to punch the third hole) but they mistakenly punched
the second hole down because Gore was listed second on the left.
Small Irritations Are Also a Problem
If you have found it difficult to relate to the catastrophic examples we have dis-
cussed so far, there are many less disastrous but still problematic examples that may
be more familiar to you. Take, for instance, the process of shutting down your com-
puter from Microsoft Windows. To do this, you have to press the Start button on the
task bar, and find the command Shut Down on the menu. Intuitively, is that where
you would expect the Shut Down command to be? What other domestic appliance,
or any other type of device, is stopped by starting it? Although the Start button may
not have been the obvious place to look for the Shut Down command when you first
used Windows, once you have used Windows for some time you adapt to what it
makes you do to shut down your computer and you just do it.
EXERCISE 1.2 (Allow five minutes)
Think about your use of the different software applications provided in the
Microsoft Office Suite or in another suite of office applications that you use (e.g.,
StarOffice from Sun). Choose one application, and think about a particular
feature that you find confusing when you use it.
DISCUSSION
Debbie writes: The application I use most often from the Microsoft Office Suite
is Word. For me, a confusing feature in more recent versions of Word is tabbed
3. The Importance of Good User Interface Design
13
Part 1
Box 1.5 A Palm Beach Voter Comments on the Disputed Ballot
Tuesday at the polls, the ballot information was very confusing if one was
voting for the Democrat. It was hard to know whom I was voting for, the way
the ballot was printed. I did not know whether I was voting for my choice, Al
Gore, or for Pat Buchanan.
That was very scary and upsetting. I had to take the ballot out a couple of times
and place it back again to be sure that the arrows pointed to the right hole; even
after the third try, I was not sure whom I was voting for, and that makes me very
mad. Many other citizens have complained regarding this situation. I am sure
this was extremely confusing for senior citizens especially.
Delia Pinto-Houbrick
From the Palm Beach Post, letters to the editor, November 10, 2000,
www.palmbeachpost.com, visited July 8, 2003.
dialogs. Specifying document settings is done via the Options tabbed dialog box,
which is accessed from the Tools menu.
Before my work computer was upgraded, I had been using Word 97 for a number
of years. In Word 97, there are only two rows of tabs for setting document options.
As there are more tabs in one row than in the other, it is easier to see and under-
stand how the tabs move when a tab is clicked on.
With greater word processing functionality, the Options dialog box became more
complex in Word 2002; there are eleven tabs in the Options dialog box arranged
in three rows of tabs. Clicking on any tab causes a puzzling rearrangement of the
tabs. In fact, each row of tabs moves as a whole; only the row positions are
changed rather than the positions of the tabs themselves, so there is some reason
to it (see Figure 1.7).
CHAPTER 1 | Introduction
14
Part 1
The Options dialogue box from the
Tools menu in Word 97
The Options dialogue box from the
Tools menu in Word 2002
Choosing the File Locations tab only makes the two
rows of tabs swap positions. The ordering of the tabs
from left to right does not change.
Choosing the Spelling & Grammar tab makes the three
rows of tabs rotate their positions. When this is done in
real time the tabs seem to scramble, and it is hard to see
that the ordering of the tabs from left to right does not
actually change.
Thus it is far easier to see and follow the movement of
the tabs in Word 97 than in Word 2002, the more
current version.
Options
Track Changes User Information Compatibility File Locations
Spelling & GrammarSavePrintGeneral EditView
Show
Draft font Bookmarks
Normal view options
File types: Location:
User InformationTrack changes Compatibility File Locations
Spelling & GrammarSavePrintGeneral EditView
?
Options
Track Changes
User Information Compatibility File Locations
Spelling & GrammarSecurity
SavePrintGeneral EditView
?
Documents C:Debs_tmpDksfilesWORD_FLZ
Clipart pictures C:__Microsoft_OfficeClipart
Show
Startup Task Pane Smart tags Windows in Taskbar
Options
User Information Compatibility File Locations
SavePrintGeneral EditView
?
Spelling
Check spelling as you type
Track ChangesSpelling & GrammarSecurity
Figure 1.7 A comparison of tabbed dialog boxes for Word 97 / Word 2002.
4 Designing for Users
With the more widespread use of computers, the knowledge, skills, and experience
of computer users have become very broad. A good user interface caters to end users
and supports them in the tasks they wish to undertake. A computer system that is
developed without a good knowledge of the users and what they want to do with the
system may be usable in that it can be used to do something, but it may not do what
the users want to do in order to achieve their goals. The system will be usable, but
not necessarily useful. This is not to say that all computer systems have to be designed
to accommodate everyone. Computer systems should be designed for the needs and
capabilities of the users for whom they are intended. Ultimately, a user should not
have to think unnecessarily about the intricacies of how to use a computer unless, of
course, that itself is the users task.
4.1 User-Centered Design
User-centered design (UCD) is an approach to user interface design and develop-
ment that involves users throughout the design and development process. User-
centered design not only focuses on understanding the users of a computer system
under development but also requires an understanding of the tasks that users will
perform with the system and of the environment (organizational, social, and phys-
ical) in which they will use the system. Taking a user-centered design approach
should optimize a computer systems usability.
Earlier we provided the ISO 9241:11 definition of usability. ISO 13407, Human-
Centered Design Processes for Interactive Systems (ISO, 1997), provides guidance on
and lists the main principles and essential activities for human (user)-centered
design, for achieving usability in systems. Briefly, the four main principles of human-
centered design are (ISO, 1997 p. 7):
1. The active involvement of users
2. An appropriate allocation of function between user and system
3. The iteration of design solutions
4. Multidisciplinary design teams
The four essential human-centered design activities are (ISO, 1997 p. 10):
1. Understand and specify the context of use
2. Specify the user and organizational requirements
3. Produce design solutions (prototypes)
4. Evaluate designs with users against requirements
Adopting the approach prescribed by ISO 13407 ensures that the users perspectives
form part of the HCI design and development process, which will positively influ-
ence the usability of the final product.
4. Designing for Users
15
Part 1
4.2 The Classic Life Cycle
User-centered design and traditional software engineering take very different
approaches to computer system design. Traditionally, software developers have
treated each phase of the software design life cycle as an independent part of soft-
ware development, which must be completely satisfied before moving on to the next
phase. This is particularly so in relation to the classic life cycle (also known as the
waterfall model, so named because of the cascade from one phase to another; see
Figure 1.8). It prescribes a predominantly sequential transition between the succes-
sive software life cycle phases, where each phase is completely satisfied before the
next begins (this is represented in Figure 1.8 by the red arrows).
This view is, of course, simplistic. Software engineers readily accept that although the
design is guided and regulated by this top-down somewhat linear model, in practice
there are many iterations up and down between stages. Sommerville (1992), for
example, has the following to say on the matter:
In practice, however, the development stages overlap and feed information to each
other. During design, problems with requirements are identified; during coding,
design problems are found; and so on. The software process is not a simple linear
model but involves a sequence of iterations of the development activities. (p. 7)
Therefore, within the software design life cycle there is a need for the phases to feed
information to each other, and for iteration, rather than the development proceed-
ing from start to finish in a simple linear fashion. This iteration is represented in
Figure 1.8 by the blue arrows. The essential difference between the classic life cycle
CHAPTER 1 | Introduction
16
Part 1
System and
software design
Requirements
definition
Operation and
maintenance
Integration and
system testing
Implementation
and unit testing
Figure 1.8 The classic life cy
