WEEK_2_User_Interdace_case_study_student.pdf

©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 1
User interface design
 Designing effective interfaces
for software systems

Objectives
 To suggest some general design principles for
user interface design
 To explain different interaction styles
 To introduce styles of information presentation
 To describe the user support which should be
built-in to user interfaces
 To introduce usability attributes and system
approaches to system evaluation

Topics covered
 User interface design principles
 User interaction
 Information presentation
 User support
 Interface evaluation

The user interface
 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

Graphical user interfaces
 Most users of business systems interact with these
systems through graphical interfaces although, in
some cases, legacy text-based interfaces are still
used

GUI characteristics
Characteristic Description
Windows Multiple windows allow different informationto be
displayed simultaneously onthe user’s screen.
Icons Icons different types of information. On some systems,
icons represent files; on others,icons represent
processes.
Menus Commands are selected froma menu rather than typed
in a command language.
Pointing A pointing device such as a mouse is used for selecting
choices froma menu or indicating items of interest in a
window.
Graphics Graphical elements can be mixed withtext on the 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

User-centred design
 The aim of this chapter is to sensitise software
engineers to key issues underlying the design
rather than the implementation of user interfaces
 User-centred design is an approach to UI design
where the needs of the user are paramount and
where the user is involved in the design process
 UI design always involves the development of
prototype interfaces

User interface design process
Executable
prototype
Design
prototype
Produce paper-
based design
prototype
Produce
dynamic design
prototype
Evaluate design
with end-users
Implement
final user
interface
Evaluate design
with end-users
Analyse and
understand user
activities

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

User interface design principles
Principle Description
User famili arity The int erface should us e terms and con cepts which are
drawnfromth e experience ofth e people who will
make mostu se ofth e system.
Consistency The int erface should b e consistent intha t, wherever
possibl e, comp arable operations should b e activ ated in
the same way.
Minim alsu rprise Users should n ever be surp rised byth e behaviou r of a
system.
Recoverability The int erface should in clude mechanisms to allo w
users to recover from errors.
User guidan ce The int erface should provid e meaningfulf eedback
whenerrors occur and provid e context-sensitiv e user
help f aciliti es.
User dive rsity The int erface should provid e appropri ate int eraction
faciliti es fordi fferenttyp es of systemus er.

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

User-system interaction
 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
 Natural language

Advantages and
disadvantages
Interaction
style
Main
advantages
Main
disadvantages
Application
examples
Direct
manipulatio
n
Fast and intui tive
interaction
Easy to learn
Maybe hard to
implement
Only suitable where
there is a visual
metaphor for tasks
and objects
Video games
CAD systems
Menu
selection
Avoids user
error
Little typing
required
Slow for
experienced users
Can become
complex if many
menuoption s
Most general-
purpose systems
Form fill-in Simple data
entry
Easy to learn
Takes up a lot of
screen space
Stock control,
Personal loan
processing
Command
language
Powerful and
flexible
Hard to learn
Poor error
management
Operating systems,
Library
information
retrieval systems
Natural
language
Accessible to
casual users
Easilyextended
Requires more
typing
Natural language
understanding
systems are
unreliable
Timetable systems
WWW
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
Method
Type
Selection
NODE LINKS FONT LABEL EDIT
JSD. example
JSD
Network
Process
Units
Reduce
cm
Full
OUIT
PRINT
Grid Busy

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
Title
Author
Publisher
Edition
Classification
Date of
purchase
ISBN
Price
Publication
date
Number of
copies
Loan
status
Order
status
NEWBOOK

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
Operating system
GUI
manager
Graphical user
interface
Command
language
interpreter
Command
language
interface

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 to
be displayed
Presentation
software
Display

Model-view-controller
Model state
Model methods
Controller state
Controller methods
View state
View methods
User inputs
view modification
messages
Model edits
Model queries
and updates

 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?
 Is there a direct manipulation interface?
 Is the information textual or numeric? Are relative
values important?

Alternative information presentations
0
1000
2000
3000
4000
Jan Feb Mar April May June
Jan
2842
Feb
2851
Mar
3164
April
2789
May
1273
June
2835

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
3
4 2
0 10 20
Dial with needle Pie chart Thermometer Horizontal bar

Displaying relative values
0 100 200 300 400 0 25 50 75 100
Pressure T
emperature

Textual highlighting
The filename you have chosen has been
used. Please choose another name
Ch. 16 User interface design
!
OK Cancel

Data visualisation
 Concerned with techniques for displaying large
amounts of information
 Visualisation can reveal relationships between
entities and trends in the data
 Possible data visualisations are:
• Weather information collected from a number of sources
• The state of a telephone network as a linked set of nodes
• Chemical plant visualised by showing pressures and
temperatures in a linked set of tanks and pipes
• A model of a molecule displayed in 3 dimensions
• Web pages displayed as a hyperbolic tree

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:
• The use of colour to communicate meaning
• Over-use of colour in the display

Colour use guidelines
 Don't use too many colours
 Use colour coding to support use 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 support
 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

Help and message system
Message
presentation
system
Error message
texts
Help
frames
Error message
system
Help
interface
Application

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 The user guidance systemshould be aware ofwhat the user is
doing and should adjust the output message to the current
context.
Experience As users become familiar with a system they become irritated
by long, ‘meaningful’ messages. However, beginners find it
difficult to understand short terse statements of the problem.
The user guidance systemshould provide both types of message
and allow the user to controlmessage conciseness.
Skilllevel Messages should be tailored to the user’s skills as wellas their
experience.Messages for the different classes of user may be
expressed in different ways depending on the terminologywhich
is familiar to the reader.
Style Messages should be positive rather thannegative. They should
use the active rather than the passive mode ofaddress. They
should never be insultingor try to be funny.
Culture Wherever possible, the designer of messages should be familiar
with the culture of the country where the systemis sold.There
are distinct cultural differences betweenEurope, Asia and
America. A suitable message for one culture might be
unacceptable in another.

Nurse input of a patient’s name
Pleas
e t
ype t
hepat
ientn
ameint
he b
o xthenc lickonOK
Bates ,J.
OK Cancel

System and user-oriented error messages
Error #27
Invalid patient id entered
?
OK Cancel
Patient J . Bates is not registered
C
lic konP ati
entsf oralistofregisteredpatients
Click on Retry to re-input a patient name
Click on Help for more information
Patients Help Retry C
an
cel
System-oriented error message
User-oriented error message

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 so good at reading screen as
they are text.

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.

Entry points to a help system
Help frame network
Top-level
entry
Entry from error
message system
Entry from
application

Help system windows
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
next topics
more
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
Help frame map
You are here
Help history
1. Mail
2. Send mail
3. Read mail
4. Redirection

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
Description of
services
Functional
description
System
evaluators
How to install
the system
Installation
document
System
administrators
Getting
started
Introductory
manual
Novice
users
Facility
description
Reference
manual
Experienced
users
Operation and
maintenance
Administrator’s
guide
System
administrators

Document types
 Functional description
• Brief description of what the system can do
 Introductory manual
• Presents an informal introduction to the system
 System reference manual
• Describes all system facilities in detail
 System installation manual
• Describes how to install the system
 System administrator’s manual
• Describes how to manage the system when it is in use

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 Description
Learnability How longdoes it take a new user to
become productive with the system?
Speed of operation How well does the system response match
the user’s work practice?
Robustness How tolerant is the systemof user error?
Recoverability How good is the systemat recoveringfrom
user errors?
Adaptability How closely is the systemtied to a single
modelof 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.

Key points
 Interface design should be user-centred. An
interface should be logical and consistent and
help users recover from errors
 Interaction styles include direct manipulation,
menu systems form fill-in, command languages
and natural language
 Graphical displays should be used to present
trends and approximate values. Digital displays
when precision is required
 Colour should be used sparingly and consistently

Key points
 Systems should provide on-line help. This should
include “help, I’m in trouble” and “help, I want
information”
 Error messages should be positive rather than
negative.
 A range of different types of user documents
should be provided
 Ideally, a user interface should be evaluated
against a usability specification

WEEK_2_User_Interdace_case_study_student.pdf

More Related Content

Similar to WEEK_2_User_Interdace_case_study_student.pdf (20)

Recently uploaded (20)

WEEK_2_User_Interdace_case_study_student.pdf