USER INTERFACE
DESIGN
Design Principles, User System interaction, Information
Presentation, User Guidance, Interface Evaluation.
The user interface
• User interfaces should be designed to match the
skills, experience and expectations of its anticipated
users.
• System users often judge a system by its interface
rather than its functionality
• A poorly designed interface can cause a user to
make catastrophic errors
• Poor user interface design is the reason why so many
software systems are never used
Human factors in interface design
• Limited short-term memory
• People can instantaneously remember about 7 items of
information. If you present more than this, they are more liable
to make mistakes.
• People make mistakes
• When people make mistakes and systems go wrong,
inappropriate alarms and messages can increase stress and
hence the likelihood of more mistakes.
• People are different
• People have a wide range of physical capabilities. Designers
should not just design for their own capabilities.
• People have different interaction preferences
• Some like pictures, some like text.
Importance of User Interface
• “Most important part of any computer system”
• “Interface is the system for most users”
• Increasingly important
• GUIs a big improvement over previous approaches
• Platforms (e.g. Mac/ Microsoft) have style guides
• 50% of code devoted to interface
• Interface should “disappear” – users can focus
on their task, not the interface
• Biggest enemy of good interface design is time
Benefits of Good Design
• Small improvements can be worth big $$$
• Interface problems are treated as bugs
• Big Improvements can establish new products,
companies, markets …
• the browser was a UI idea – before it, search using
gopher etc was tedious.
• AOL was successful because it was more user
friendly than early leader CompuServe.
GUI characteristics
Characteris ti c Des cripti on
Win dows Multiple windows allow different information t o be
displayed simult aneously on th e user’s screen.
Icon s Icon s differen t ty pes of informationOn. some sy st ems,
icon s represent files; on ot hers, icon s represen t
processes.
Men us Co mmands are select ed fro m a menu rat her than t yped
in a command lan guage.
Po int ing A point ing device such as a mo use is used for select ing
ch oices from a men u or indicat ing it ems o f in terestin a
window.
Graph ics Graph ical elemen ts can be mix ed wit h text on t he same
display.
GUI advantages
• They are easy to learn and use.
• Users without experience can learn to use the system
quickly.
• The user may switch quickly from one task to another
and can interact with several different applications.
• Information remains visible in its own window when
attention is switched.
• Fast, full-screen interaction is possible with immediate
access to anywhere on the screen
GUI characteristics
• Windows
• Icons
• Menus
• Pointing
• Graphics
Cont..
Advantages
• They are easy to learn and use.
• Users without experience can learn to use the system quickly.
• The user may switch attention between tasks and applications.
• Fast, full-screen interaction is possible with immediate access
to the entire screen
Problems
• A GUI is not automatically a good interface
• Many software systems are never used due to poor UI design
• A poorly designed UI can cause a user to make catastrophic
errors
UI design principles
• UI design must take account of the needs, experience and capabilities of the system users.
• Designers should be aware of people’s physical and mental limitations (e.g. limited short-
term memory) and should recognise that people make mistakes.
• UI design principles underlie interface designs although not all principles are applicable to
all designs.
Design principles
• User familiarity
• The interface should be based on user-oriented terms and concepts rather than computer
concepts. For example, an office system should use concepts such as letters, documents, folders
etc. rather than directories, file identifiers, etc.
• Consistency
• The system should display an appropriate level of consistency. Commands and menus should
have the same format, command punctuation should be similar, etc.
• Minimal surprise
• If a command operates in a known way, the user should be able to predict the operation of
comparable commands
Design principles
• Recoverability
• The system should provide some resilience to user errors and allow the user to recover from
errors. This might include an undo facility, confirmation of destructive actions, 'soft' deletes, etc.
• User guidance
• Some user guidance such as help systems, on-line manuals, etc. should be supplied
• User diversity
• Interaction facilities for different types of user should be supported. For example, some users
have seeing difficulties and so larger text should be available
Design issues in UIs
• Two problems must be addressed in interactive systems design
• How should information from the user be provided to the computer system?
• How should information from the computer system be presented to the user?
• User interaction and information presentation may be integrated through a coherent
framework such as a user interface metaphor.
Interaction styles
• Direct manipulation
• Menu selection
• Form fill-in
• Command language
Interaction styles
Interaction Main advantages Main disadvantages Application
style examples
Direct Fast and intuitive May be hard to Video games
manipulation interaction implement CAD systems
Easy to learn Only suitable where
there is a visual
metaphor for tasks and
objects
Menu Avoids user error Slow for experienced Most general-purpose
selection Little typing users systems
required Can become complex if
many menu options
Form fill-in Simple data entry Takes up a lot of screen Stock control,
Easy to learn space Personal loan
processing
Command Powerful and Hard to learn Operating systems,
language flexible Poor error management Library information
retrieval systems
Direct manipulation advantages
• Users feel in control of the computer and are less likely to be intimidated by it
• User learning time is relatively short
• Users get immediate feedback on their actions so mistakes can be quickly detected and
corrected
Direct manipulation problems
• The derivation of an appropriate information space model can be very difficult
• Given that users have a large information space, what facilities for navigating around that
space should be provided?
• Direct manipulation interfaces can be complex to program and make heavy demands on
the computer system
Control panel interface
Title JSD. example Grid Busy
Method JSD
OUIT
Type Network Units cm
Selection Process Reduce Full
PRINT
NODE LINKS FONT LABEL EDIT
Menu systems
• Users make a selection from a list of possibilities presented to them by the system
• The selection may be made by pointing and clicking with a mouse, using cursor keys or by
typing the name of the selection
• May make use of simple-to-use terminals such as touchscreens
Advantages of menu systems
• Users need not remember command names as they are always presented with a list of valid
commands
• Typing effort is minimal
• User errors are trapped by the interface
• Context-dependent help can be provided. The user’s context is indicated by the current
menu selection
Problems with menu systems
• Actions which involve logical conjunction (and) or disjunction (or) are awkward to represent
• Menu systems are best suited to presenting a small number of choices. If there are many
choices, some menu structuring facility must be
used
• Experienced users find menus slower than command language
Form-based interface
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Command interfaces
• User types commands to give instructions to the
system e.g. UNIX
• May be implemented using cheap terminals.
• Easy to process using compiler techniques
• Commands of arbitrary complexity can be
created by command combination
• Concise interfaces requiring minimal typing can
be created
Problems with command interfaces
• Users have to learn and remember a command language. Command interfaces are
therefore unsuitable for occasional users
• Users make errors in command. An error detection and recovery system is required
• System interaction is through a keyboard so typing ability is required
Command languages
• Often preferred by experienced users because they allow for faster interaction with the
system
• Not suitable for casual or inexperienced users
• May be provided as an alternative to menu commands (keyboard shortcuts). In some cases,
a command language interface and a menu-based interface are supported at the same time
Natural language interfaces
• The user types a command in a natural language. Generally, the vocabulary is limited and
these systems are confined to specific application domains (e.g. timetable enquiries)
• NL processing technology is now good enough to make these interfaces effective for casual
users but experienced users find that they require too much typing
Multiple user interfaces
Graph ical u ser Un ix sh ell
inter face inter face
(Gno me/KD E) (ks h/cs h)
X-wind ows GUI Co mmand
mana ger lan gu age
interpreter
Linu x o peratin g sy stem
Web-based interfaces
• Many web-based systems have interfaces
based on web forms.
• Form field can be menus, free text input,
radio buttons, etc.
Information presentation
• Information presentation is concerned with presenting system information
to system users
• The information may be presented directly (e.g. text in a word processor) or
may be transformed in some way for presentation (e.g. in some graphical
form)
• The Model-View-Controller approach is a way of supporting multiple
presentations of data
Information presentation
Information to Presentation
be displayed software
Display
Information presentation
• Static information
• Initialised at the beginning of a session. It does not change during the session
• May be either numeric or textual
• Dynamic information
• Changes during a session and the changes must be communicated to the system user
• May be either numeric or textual
Information display factors
• Is the user interested in precise information or data relationships?
• How quickly do information values change?
Must the change be indicated immediately?
• Must the user take some action in response to a change?
• Does the user need to interact with the displayed info via a direct manipulation interface?
• Is the information textual or numeric? Are relative values important?
Alternative information presentations
Jan Feb Mar April May June
2842 2851 3164 2789 1273 2835
4000
3000
2000
1000
0
Jan Feb Mar April May June
Analogue vs. digital presentation
• Digital presentation
• Compact - takes up little screen space
• Precise values can be communicated
• Analogue presentation
• Easier to get an 'at a glance' impression of a value
• Possible to show relative values
• Easier to see exceptional data values
Dynamic information display
1
0 10 20
4 2
Dial with needle Pie chart Thermometer Horizontal bar
Displaying relative values
Pressure Temper atu re
0 100 200 300 400 0 25 50 75 100
Textual highlighting
Data visualisation
• Concerned with techniques for displaying large amounts of information
• Visualisation can reveal relationships between entities and trends in the data
Colour displays
• Colour adds an extra dimension to an interface and can help the user understand complex
information structures
• Can be used to highlight exceptional events
• Common mistakes in the use of colour in interface design include over-use of colour in the
display
Colour use guidelines
• Don't use too many colours
• Use colour coding to support user tasks
• Allow users to control colour coding
• Design for monochrome then add colour
• Use colour coding consistently
• Avoid colour pairings which clash
• Use colour change to show status change
• Be aware that colour displays are usually lower
resolution
User guidance
• User guidance covers all system facilities to support users including on-line help, error
messages, manuals etc.
• The user guidance system should be integrated with the user interface to help users when
they need information about the system or when they make some kind of error
• The help and message system should, if possible, be integrated
Error messages
• Error message design is critically important.
Poor error messages can mean that a user
rejects rather than accepts a system
• Messages should be polite, concise, consistent
and constructive
• The background and experience of users
should be the determining factor in message
design
Design factors in message wording
• Context
• Experience
• Skill Level
• Style
• Culture
Design factors in message wording
Context The user guidance system should be aware of what the user is
doing and should adjust the out put message t o t he current
cont ext .
Experience As users become familiar with a system t hey become irrit at ed
by long, ‘meaningful’ messages. However, beginners find it
difficult to understand short t erse statement s of t he problem.
The user guidance system should provide bot ht ypes of message
and allow the user t o control message conciseness.
Skill level Messages should be tailored t o t he user’s skills as well as their
experience. Messages for the different classes of user may be
expressed in different ways depending ont he terminology which
is familiar t o the reader.
St yle Messages should be positive rat her than negative. They should
use t he active rat her t han t he passive mode of address. They
should never be insult ing or t ry t o be funny.
Cult ure Wherever possible, thedesigner of messages should be familiar
with t he culture of t he count ry where t he system is sold. There
are distinct cult ural differences between Europe, Asia and
America. A suit able message for one cult ure might be
unacceptable in another.
System and user-oriented error messages
User -o rien ted er ror messag e
System-or iented err or messag e
Er ror #27
?
Patient J . Bates is n ot r egistered
Invalid patient id entered C k l ai otc o ni r e Pn a t s l i f s t o
Click on Retry to re-input a patient name
Click on Help for more information
O K Cancel
Patients Help Retry C a n c e l
Help system design
• Help? means “ Help I want information”
• Help! means “HELP. I'm in trouble”
• Both of these requirements have to be taken
into account in help system design
• Different facilities in the help system may be
required
Help information
• Should not simply be an on-line manual
• Screens or windows don't map well onto paper
pages.
• The dynamic characteristics of the display can
improve information presentation.
• People are not as good at reading screen as
they are paper text.
• Content should be prepared with help of application specialists
• Content should not be too large – don’t overwhelm user
Help system use
• Multiple entry points should be provided so that the user can get into the help system from
different places.
• Some indication of where the user is positioned in the help system is valuable.
• Facilities should be provided to allow the user to navigate and traverse the help system.
• Index, TOC, and Search should be provided
Entry points to a help system
Top-level
entry
Entry from
application
Entry from error
message system
Help frame network
Help system windows
Help frame map Mail redirection
Mail may be redirected to another
network user by pressing the
redirect button in the control
panel. The system asks for the
name of the user or users to
whom the mail has been sent
You are here more next top ics
Help history
1. Mail
2. Send mail
3. Read mail
4. Redirection
Help on WWW
• Easy to implement
• Easy for users to use
• Difficult to link to applications themselves
• users may need to make extra effort to get to help
• Help doesn’t know context where you needed help – cannot provide context sensitive
help
User documentation
• As well as on-line information, paper
documentation should be supplied with a system
• Documentation should be designed for a range of
users from inexperienced to experienced
• As well as manuals, other easy-to-use
documentation such as a quick reference card
may be provided
User document types
System System Novice Experienced System
evaluators administrators users users administrators
Functional Installation Introductory Reference Administrator’s
description document manual manual guide
Description of How to install Getting Facility Operation and
services the system started description maintenance
User interface evaluation
• Some evaluation of a user interface design should
be carried out to assess its suitability
• Full scale evaluation is very expensive and
impractical for most systems
• Ideally, an interface should be evaluated against a
usability specification. However, it is rare for such
specifications to be produced
Usability attributes
Attribute Des cripti on
Learnability How long does it t ake a new user to
become product ive with t he system?
Speed of operat ion How well does t he system response match
t he user’s work practice?
Robust ness How t olerant is the syst em of user error?
Recoverability How good is t he syst em at recovering from
user errors?
Adapt ability How closely is t he system t ied t o a single
model of work?
Simple evaluation techniques
• Questionnaires for user feedback
• Video recording of system use and subsequent
tape evaluation.
• Instrumentation of code to collect information
about facility use and user errors.
• The provision of a grip button for on-line user
feedback.
Things to Test
• Conformance with a requirement
• Conformance with guidelines for good design
• Identification of design problems
• Ease of system learning
• Retention of learning over time
• Speed of task completion
• Speed of need fulfillment
• Error rates
• Subjective user satisfaction
…System - User Interface Design Goals
• 5 human factors central to community evaluation:
• Time to learn
• Speed of performance
• Rate of errors by users
• Retention over time
• Subjective satisfaction
• Trade-offs sometimes necessary
• Test all design alternatives using mock-ups
Objective Measures of Usability
• Effectiveness
• Speed of performance, # errors (against some standard)
• Tasks completeable by required pct of target users
• Learnable
• Time to learn, amount of training and tech support needed (against some standard)
• Relearning time for intermittent users
• Flexible
• Subjective satisfaction
• Tiredness, discomfort, frustration, effort required, willingness/eagerness to use system
Simple evaluation techniques
• Questionnaires for user feedback
• Video recording of system use and subsequent tape evaluation.
• Observation of users at work with system and “thinking aloud” about how they are trying
to use system
• Instrumentation of code to collect information about facility use and user errors.
• The provision of a gripe button for on-line user feedback.
Kinds of Tests
• Guidelines review
• Heuristic evaluation (will be covered last due to extensive coverage)
• Cognitive walkthrough
• Think aloud evaluations
• Usability test
• Classic experiments
• Focus groups
