a computer-based system
are designing a computer-based system, you need to
consider more than just the electronic components that
make up the computer itself. You should think of all the
stages that the system will go through, such as design,
manufacture and use. For each stage, you will need to
think of all the people that might come into contact
with the system - these are the 'users'. You need to
consider all the various tasks that they will carry out,
what additional equipment that they might need and where
they will perform their tasks. There must be a good
match between the user, the task, the equipment and the
environment, for the system to be effective and achieve
could use a step-by-step approach to make sure that you
consider everything and give yourself the best chance of
designing a successful system. We will use a digital
camera as an example of a computer-based system
throughout the following steps. Please note that the
considerations given for the camera example are in no
way complete, but are there to give you starting points.
all the aims of the system.
are the main functions of the system? What are the
individual tasks that make up the main functions? You
will need to break these down into as much detail as you
can at this stage.
Task description is an essential first consideration when designing a system. The task description may be based on previous
similar systems, where they exist. For example, there is a long history of designing cockpit instrumentation. In this case, the designers may have a relatively precise
idea very early in the design about the information that is required and the controls that must be
provided. On the other hand, the design of games consoles demands innovative thinking as the technology for handling images
main functions are to record digital photographs and
video. The individual tasks include opening the lens
cover, focusing on the subject, opening the shutter, recording and storing the image, closing the lens cover.
We also want to include the use of flashlight, viewing
and editing the recorded images, and giving a choice of
what tasks the system is to carry out, and what tasks
the user is to carry out.
is called 'allocation of function'. It is where you
start to think about the abilities of the users and the
system in greater detail. What is the user capable of
doing to meet the aims of the system? The tasks that the
system carries out depend largely on the level of
technology available. It also depends on how much you
want to 'automate' the system, and how much you want to
leave to the user to carry out and control.
Automation is the process where a task, previously carried out by a user, is to be carried out by the equipment.
There are a number of things that people are better at
doing than computer-based systems, and the other way
around. Obviously, people can think, make decisions and
react to what is happening around them, computers only
ever do what they are programmed to do, without change
(unless they break down). This is one strength of a
computer, it does not get tired, and if programmed well,
it is consistent and does not make mistakes.
tasks for the user difficult or complicated? Will they
need much training or instruction? Once they learn how
to do the task, will they do it often enough that they
won't need reminding? Do the users need particular
skills or attributes, such as strength?
need to think about maintenance at this point too. Will
there be automatic fault-finding in your system or will
someone need to track down faults? Would automating
certain tasks introduce new technology? Would this mean
that the system might break down and need repair more
stage, you may start to meet 'constraints' - things that
restrict what you want to do. It may be cost; you might
want a task to be carried out by the system that would
add to the cost of manufacture so much that it would
make it too expensive for people to buy. You might have
no choice but to give that task to the user. Another
constraint may be time; you might have a deadline to
meet for producing your system and to introduce an
automatic task might mean additional research and
development that means you would miss your deadline.
want the user to focus on the subject or do you want the
camera to do it? Will the user be able to focus
properly? What if their sight is not good? Might
children use the camera? Will they know that they have
to focus? Are there times when the user would want to
focus manually? Should we give them the option of both
automatic and manual focus? What about the flash? Should
it operate automatically when lighting levels are low or
should the user switch it on? How will the user know if
the lighting is not good enough?
which are the best methods for control of the system and
display of information, based on matching the user to
the task, additional equipment and the environment.
is where you will need to consider your user's abilities
and limitations in great detail. If the system has many
complicated functions, it may need several control
devices and several displays giving information about
the status of the system. Each control and display will
need to be matched to the user in terms of size,
operation and understanding. See the topics on controls
and displays for details.
These features, together with the size of the remaining
components, will determine the overall size of the
system. Users may be able to carry the system around and
use it (mobile phone), they may need or want to sit down
to use it (supermarket checkout), or they may need to
stand to see and reach all the features (power station
control panel). You will need to think about positioning
of controls and displays so that the user can see and
reach everything they need to. If the system is
portable, is it light enough for all users to carry it
around when they need or want to, without strain?
flow should be considered. What does the user need to
know and be able to communicate to the system, and what
information does the user need from the system? The user
can get information from the system in the form of light
in a display, or sound, as in an alarm. Knowledge is created when the user
receives the information, interprets its meaning, and turns it into an understanding of the
system. Communication between the user and the system
should be simple and quick. The rate at which information
the user and the system is an important characteristic of the system. The user may act infrequently, or there may a continuous interaction like a conversation.
The overall effectiveness of the system will depend on how
well the control devices match the task design. Some tasks are likely to be performed better with some
types of controls than others:
a joystick, trackerball or mouse to move a cursor on
a keyboard or keypad to enter numbers or letters
a lightpen or touchscreen for immediate selection of items on
speech when the system can translate it into
may be several reasons for choosing one
control device over another. These may include the abilities of the users.
The first three types of devices above depend on
hand-eye co-ordination. Therefore, if the users are likely to have poor vision or poor hand control, then speech may become an important alternative. Similarly, if the users are likely to be busy
with many hand controls, then foot controls or speech
may be more effective.
important to match features of the system to the way
that users think, and to take account of their prior
experience and expectations. If there is already a
successful and well-known method of doing something,
consider using it for your system. There is no problem
with finding an alternative way of carrying out a task
if it is an improvement, but it should not run against
what the user might expect. In this case, users may make errors or become
frustrated. An example is the three small boxes with
symbols in them in the top right hand corner of windows
on your computer screen. You know that they mean
minimise, maximise and close window. It would be very
frustrating to find that these functions have changed
around and you closed a file when you meant to minimise
it, for example.
need to consider any other equipment that might have to
be used with the system to achieve the system's aims,
and make sure that the equipment is compatible with the
system and the user.
system is to be operated by several people at once, or
as part of a group of systems, then communication and
interaction between all the users should be considered
too. Will they need to talk to each other? Will they be
close enough to hear? Will they need to use telephone or
radios to talk to each other? This is where the physical
environment will be important too. Will noise levels
enable people to hear speech or alarms?
lighting be good enough to see displays?
Lighting is a vital consideration as a display may be used in an areas
where lighting varies hugely. For example, there is high illumination
in an airport control tower during the day, with wide
windows letting in lots of natural light,
and low artificial lighting at night when the users may want to see out of the
windows while at the same time using the display. This
may mean designing a special workstation that has
screening, or equipping the display with a light
intensity adjustment. These are sometimes provided in
cars to enable dashboard lights to be dimmed.
the system emit heat? Will it need special ventilation?
Will it be used in particularly hot or cold
environments. Will this affect the system, or the user?
See the temperature
topic for more information about suitable working
many controls will there be? Can they all fit on the
camera and leave room to hold it without inadvertently
operating one? Can controls be doubled up? Will this be
confusing? Can all the information about the photographs
and settings be displayed on one screen? Will the text
be large enough? Will users understand symbols or do we
need whole words? There needs to be a connection between
the camera and a computer to download the photographs.
Will this be a cable or will the camera plug directly
into the computer, or a base unit? Will a cable have a
standard connection? Will users understand what to do
with it? Does the display light up for use in the dark?
Does the camera need to be kept out of the sun, but not
left in the cold?
and build the system.
types of displays and controls in general,
you will need to specify the information to be provided on the displays and the precise means of exercising control.
There are several ways of positioning displays and
controls that will be helpful to the user. You will need
to find out the information and knowledge required simultaneously, so that
displays and controls can be grouped together. You also
need to check the performance required in frequent, important or critical tasks to ensure that it is possible for the user to achieve the required
levels and carry out the tasks. For example, will the
user be quick enough to operate several controls in a
certain sequence, in a certain time, if necessary?
Ensure, too, that there is appropriate feedback to the
user so that they have confirmation of their actions.
detailed design of the screens for the system could
conform to a 'style guide'. Style guides are detailed specifications of all the
features, and are created and developed for two
- To make the equipment recognisable as belonging to a particular
- To standardise the operation of
a system and make it easy for the user to learn, or
to bring their previous skills and learning into use.
examples of software now use the familiar style of
windows, menus and icons, as this reduces learning time
and programmers can concentrate on improving the
functions of a system rather than the way it is used.
International standards should be used where relevant
for symbols, signs and colours.
The design of
alarms and warnings needs to be considered very carefully, as they may have safety or operational implications,
for example, lights or sounds may be used to warn
drivers that a car door has been left open, or the car lights left switched on.
all possible, and time and money allow, build a mock-up
of the entire system, or elements of it, and use it to
try out the match between users and the system. It is
quick and easy to test users' perceptions about the
meanings of symbols - this can even be paper-based.
Workstations can be mocked up full-size using cheap
materials to make sure that displays and controls are
within sight and reach of users. Feedback at this stage
is invaluable and will improve the potential success of
camera will include a cable for connection to a computer
and software to allow photographs to be downloaded from
the camera to the computer. Standard computer connectors
will be used to ensure compatibility with a high
percentage of computers. A battery charger will be
provided and a memory card to enable users to be able to
operate the camera with no additional purchases. The
camera will use menus and will give feedback to users by
emitting a beep when menu selections are made.
install and evaluate the system
sure that users can work the system to carry out the
listed tasks and achieve the original aims. Test the
system with a variety of users in real conditions. Make
sure the system is safe. See the topic on product
evaluation for more details.
The performance and effectiveness
of a system should be checked. You should consider
whether the system performs as specified. For example,
if printing is a feature, does it provide a printout within a specified time when
requested? What is the error rate? Is it acceptable?
What are the causes of errors? Are they system or user
errors? Are user errors due to mismatches between the
user and the system?
picture quality good enough? Is download of photographs
successful? Is the casing strong enough to withstand
outdoor use? How many times can the battery be recharged
before it needs to be replaced?
users with training, instruction and support
||All systems need to have trained users before they can work effectively. Similarly they all need some maintenance and support even if it is only changing
an ink cartridge in a printer or putting disks away carefully.
that users have all the information they need to operate
the system. If the system is complicated, users should
be given scenarios to enable practice without serious
consequences for error. The amount of training and
instruction needed will depend on the user and their
knowledge and prior experience, and the complexity of
the system. Users should be given training in a form and
amount that they understand and are confident with.
Where performance is critical, it may be necessary to use simulators of actual operational conditions so that training can take place in a safe environment.
For example, pilots can practice in flight simulators. Exercises may be conducted with larger systems to enable
users to develop skills and knowledge in handling infrequent or hazardous operations. These might include medical response teams reacting to major emergencies. Military and public services exercise regularly to ensure that skills and knowledge are maintained in the use of large scale computer-based systems.
maintenance manuals for complex systems. This should
include removal (and possible dismantling) of the system. Troubleshooting guides
are useful for home users of computer-based systems if
solutions can be carried out by them without risk to
should be given information about hazards - their
effects and how to avoid them. This information should
include disposal instructions, especially if there is
hazardous material involved, for example, batteries.
instruction booklet will be provided that includes use
of software and computer connections. Use of the display
will be shown in picture and text format. Battery and
memory card maintenance will be explained. A simple
troubleshooting guide will be included with contact
information for further help.