Karolina Muszyńska
Based on: I. Sommerville, „Inżynieria oprogramowania”
1. Universal principles of user interface design
2. Five ways to interact with an information
system
3. Methods of information processing and the
correctness of graphical presentation
4. The basic principles of designing the builtin help system for the user
5. Usability attributes and a simple approach to
the assessment of the system interface
2
 A good user interface design is a prerequisite for
a good system
 An interface which is difficult to use will in the
best case lead to many mistakes, in the worst
case users will simply refuse to use the system,
regardless of its functionality
 If the information is presented in a confusing
and misleading way, users will misinterpret the
system commands and may execute a sequence
of commands that can damage data or lead to
system failure
3
 Nowadays almost all computer users have
computers that offer graphical user interface
(GUI) that supports high resolution color screen
and interaction using mouse and keyboard or
touch screen
4
Characteristics
Description
Windows
Multiple windows allow to simultaneously display
different information on the user's screen
Icons
Icons represent different types of information; in
some systems they correspond to files, and in
others to processes
Menu
Commands are selected from the menu and not
written in a form of command instructions
Pointing
Pointing devices such as a mouse are used to select
a menu item and to point to required elements on
the screen (we can also use our finger on a touch
screen)
Graphics
Graphic elements can be combined with text on the
same screen
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 They are fairly easy to learn and to use. Users
without experience with computers can learn
how to use the interface within a short training
 The user has several screens (windows) to
interact with the system. You can go from one
task to another without losing the overview of
the information prepared during the first task
 Fast interaction using full-screen which gives
you access to any place on the screen
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Analyze
and recognize
user actions
Develop
a paper
prototype
Evaluate the
prototype
with users
Designed
prototype
Build a dynamic
prototype
Executable
prototype
Evaluate the
prototype
with users
Implement the
final interface
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 User interface designers must take into account
the physical and mental abilities of people who
will be using the software
 People have limited memory and make mistakes
especially when they have to handle a large
amount of information or are under pressure
 People have different mental capabilities
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Principle
Description
The
structure
principle
Design should organize the user interface purposefully,
in meaningful and useful ways based on clear, consistent
models that are apparent and recognizable to users,
putting related things together and separating unrelated
things
The
simplicity
principle
The design should make simple, common tasks easy,
communicating clearly and simply in the user's own
language, and providing good shortcuts that are
meaningfully related to longer procedures
The
visibility
principle
The design should make all needed options and
materials for a given task visible without distracting the
user with extraneous or redundant information. Good
designs don't overwhelm users with alternatives or
confuse with unneeded information
Usage-centered design introduced by Larry Constantine and Lucy Lockwood
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Principle
Description
The
feedback
principle
The design should keep users informed of actions or
interpretations, changes of state or condition, and errors
or exceptions that are relevant and of interest to the
user through clear, concise, and unambiguous language
familiar to users
The
tolerance
principle
The design should be flexible and tolerant, reducing the
cost of mistakes and misuse by allowing undoing and
redoing, while also preventing errors wherever possible
by tolerating varied inputs and sequences and by
interpreting all reasonable actions
The reuse
principle
The design should reuse internal and external
components and behaviors, maintaining consistency with
purpose rather than merely arbitrary consistency, thus
reducing the need for users to rethink and remember
Usage-centered design introduced by Larry Constantine and Lucy Lockwood
10
 Close to user principle - users should not be
forced to adapt to the interface to make it easier
to implement. The interface should use the
categories known to the user, and the objects
processed by the system should be directly
related to the users’ environment
 No surprises principle - users should not be
surprised by the behavior of the system, because
they get irritated when the system reacts in an
unexpected way
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 Consistency principle - system commands and
menus should have the same format. Command
parameters should always be provided in the same
way. Consistent interfaces reduce learning time.
Interface consistency within a group of
subsystems is also crucial. If possible, commands
of similar meaning should be expressed in the
same way in all subsystems. Errors often result
from assigning different meanings to the same
key combinations (i.e. „ctrl-b”) in a group of
subsystems
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 User interface designer has to deal with
two major issues:
◦ How to provide information from the user to the
computer system?
◦ How to present information generated by the
computer system to the user?
 Consistent user interface must integrate
user interaction and presentation of
information
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 Direct action
 Choice from menu
 Completing a form
 Command language
 Natural language
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Interaction
Advantages
Disadvantages
Examples
Direct action Fast and intuitive
May be difficult to
implement; suitable only if
there is a graphic
representation of objects
and activities
Video games, CAD
systems
Choice from
menu
Avoids user error;
requires little
writing
Too slow for experienced
users; can be complicated
when there are many menu
options
Most of the general
purpose systems
Completing
a form
Simple data input;
easy to learn
Uses a large area of the
screen
Warehouse
management; loans
processing
Command
language
Reliable and
flexible
Difficult to learn; small
error handling capabilities
Operating systems;
information library
extract systems
Natural
language
Available for
casual users; easy
to expand
Requires more writing;
unreliable natural language
recognition systems
Timetables (trains)
systems, web
information
specifying systems 15
interaction; easy
to learn
 Does the user need precise information or just
relationships between data values?
 How quickly does the information change? Does
the user need to see these changes immediately?
 Must the user take some action in response to a
change?
 Should the user react to the displayed information
through a direct action interface?
 Is the displayed information textual or numeric?
Are relative values important?
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 Text-based data takes up less space than
graphically displayed information
 Dynamically changing numerical information is
reflected best by using graphical presentation
 Constantly changing digital displays are
misleading, because fast assimilation of accurate
information is difficult
 For presenting exact alphanumeric information
graphics can be used to extract data hidden in the
background
 Graphic highlighting may also serve to draw user’s
attention to changes in parts of the image
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 Proper use of color can improve the interface,
helping users to understand and master the
complexity of the system
 It is however easy to misuse color and create
an interface graphically unattractive and
causing errors
 Interface designers should adopt a general
principle that the colors should be used with
caution
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 Limit the number of colors used and use them
carefully
 Use color change to indicate changes in the
system
 Use a color code that will help the user in the
realization of tasks
 Use color coding consistently and sensibly
 Beware of the relationships between colors one of the worst possible color combination is
red background and blue text
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 Avoid using whole sentences – use „Quit”
instead of „Press this button to Quit”
 Symbols and icons should replace text where
possible
 Commonly used symbols should be used, also
symbols known from everyday life (for
example road signs)
 Use simple and readable font –max two
different styles, max three different sizes (do
not minimize the font to make the text fit the
screen)
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1. Messages generated by the system in
response to user actions
2. Instant help system
3. Documentation available in the system
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 The first user experience in dealing with the
system depends on the system error
messages
 Inexperienced users who work with the
system for the first time make mistakes and
need to understand the error messages
immediately
 When designing error messages the past
experience of users should be taken into
account
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Issue
Description
Context
User support system should take into account current user
actions and adapt its messages to the current context
Experience As the user gets familiar with the system, he can be irritated
with too long messages. However, novice users have difficulty
in understanding brief and concise problem definitions. User
support system should therefore be able to display both types
of messages, depending on the user's awareness/experience
Skills
Messages should be tailored to the user's skills and his
experience. Messages for different user groups can be
expressed in different ways depending on the terminology that
is know to them
Style
Messages should be positive, not negative. They should never
be malicious or humorous
Culture
As far as possible, the designer of messages should be familiar
with the culture of the country in which the system will be sold.
Between Europe, Asia and America there are various cultural
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differences
Insert second and first name of the patient and press OK
Brown John
OK
Cancel
24
Error message written
in the system categories
Error message written
in the user categories
Patient Brown John is not registered
?
Error 27
Invalid patient identifier
OK
Press Patients button to see the list of
registered patients.
Press Repeat button to insert the patients
data once again.
Press Help button to get more information
Cancel
Patients
Repeat
Help
Cancel
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 Audio messages should be used only if the
user cannot look at the screen or is away from
the computer
 Messages should include first the goal and
then the activity – „To start the application
press Enter”
 There should be a possibility to quite listening
to messages at any time, as well as to replay
them
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 They should be prepared with the participation of
specialists in the field of application
 Help topic should not be a simple representation
of the user's guide, because people read
information on the screen differently than paper
documentation
 The text, its layout and style should be carefully
marked to make it possible to read in a fairly small
window
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 They can be implemented as a set of related Web
sites or by using a universal hypertext system,
integrated with application programs
 The hierarchy can be easily browsed by selecting
parts of the message marked as links
 Website-type help systems can be easily
implemented and there are no specific software
requirements
 Help systems should have several different entry
points (from the program, from the system error
messages)
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 User’s documentation is not strictly part of the
user interface design
 It is however a good practice to design instant
help system in conjunction with the paper
documentation
 User manuals should include more detailed
information than the help system provides
 They should be designed in such a way that
they can be used by different classes of users.
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System
reviewers
System
administrators
Functional
description
Installer
manual
Basic manual
Service
description
How to install
the system
Initial work
with the system
Novice users
Experienced
users
Manual
System
administrators
Administrator
manual
Description of Operation and
facilities
maintenance
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 Evaluation of the interface is the process of
estimating interface usability and verifying if it
meets the requirements of the user
 Evaluation of the interface should therefore be part
of the normal process of verification and validation
of systems
 The assessment should be done with respect to
the usability specification which determines the
usability attributes
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Attribute
Description
Ease of
learning
How much time does it take a new user to effectively use
the system?
Speed of
operation
To what extent does the efficiency of the system meet the
work practice of users?
Reliability
How does the system handle users’ errors?
Undo
possibilities
How well does the system cope with undoing the results
of users’ mistakes?
Adaptation
possibilities
How firmly is the system associated with a certain work
model?
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 Questionnaires asking the users what they think
about the interface
 Watching the users work with the system and try
to achieve a certain goal or realize a certain task
 Short films with typical uses of the system
 Collecting information on the most commonly
used system facilities and the most common
mistakes by installing a monitoring software
application
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 User interface design process should focus on the user.
The interface should communicate with the user using
language, terms and style that is know to him. It should
be logical and consistent. It should include facilities to
help users work with the system and undo mistakes
 Five main methods of interaction with the system
include direct action, choice from menu, filling a form,
command language and natural language
 The information should be displayed graphically when
you want to present trends and approximate values.
Digital displays should only be used when precision is
required
 The user interface colors should be used carefully and
consistently. Designers should take into account that
some part of users is color-blind
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 Help systems should offer two types of support:
assistance when the user has a problem with the
system and help that provides him with information on
a selected topic
 Error messages should not suggest that the user is
guilty. They should rather suggest how to fix the error
and include a link to the help system
 User’s documentation should include guides for
beginners and manuals. Separate documentation for the
administrators should also be provided
 The system specification should include (where
possible) quantitative values of usability attributes. The
evaluation process should include the verification of the
system with respect to these requirements
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