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©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 1

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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
Software engineers generally must do interface design
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 4

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“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
Software Engineering, 6th edition. Chapter 15
Galitz
Slide 5 ©Ian Sommerville 2000

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Small improvements can be worth big $$$
• Book e.g. if users work 1 sec slower on each of 4.8 million screens per year, need almost an extra person
• Book e.g.s Redesigns have improved productivity 20%, 25%, 40%, 50% …
• IBM - $1 invested in usability returns $10-$100
Interface problems are treated as bugs
• Pressman - $1 fix during design, $10 fix during development, $100 fix after release
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.
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15
Galitz
Slide 6

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Most users of business systems interact with these systems through graphical interfaces although, in some cases, legacy text-based interfaces are still used
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 7

•Windows
•Icons
•Menus
•Pointing
•Graphics
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 8

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They are easy to learn and use.
The user may switch quickly from one task to another and can interact with several different applications.
Fast, full-screen interaction is possible with immediate access to anywhere on the screen
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 9

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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
Slide 10 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

Analyse and understand user activities
Produce paperbased design prototype
Evaluate design with end-users
Design prototype
Produce dynamic design prototype
Executable prototype
Evaluate design with end-users
Implement final user interface
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 11

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 12

Principle Description
User Familiarity Interface should use terms familiar to users
Consistency Comparable operations should be started the same way
Minimal Surprise Users should never be surprised
Recoverability
User Guidance
User Diversity
Users should be able to recover from their errors
Meaningful feedback, context-sensitive help
Should provide for different types of user
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 13

Nielsen’s Ten Usability Heuristics
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Visibility of system status
Match between system and the real world
User control and freedom
Consistency and standards
Error prevention
Recognition rather than recall
Flexibility and efficiency of use
Aesthetic and minimalist design
Help users recognize, diagnose, and recover from errors
Help and documentation Nielsen
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 16

7.
8.
3.
4.
1.
2.
5.
6.
9.
10.
Automate unwanted workload
Reduce uncertainty
Fuse data
Present new info with meaningful aid to interpretation
Use names that are conceptually related to functions
Group data in consistently meaningful ways to reduce search time
Limit data-driven tasks
Include in displays only info needed by user at a given time
Provide multiple coding of data where appropriate
Practice judicious redundancy
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

6.
7.
8.
4.
5.
9.
1.
2.
3.
Speak the user’s language
Be consistent
Minimize the user’s memory load
Build flexible and efficient systems
Design aesthetic and minimalist systems
Use chunking
Provide progressive levels of detail
Give navigational feedback
Don’t lie to the user
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15
Galitz
Slide 18

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 19

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Direct manipulation
Menu selection
Form fill-in
Command language
Natural language
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 20

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Users feel in control of the computer and are less likely to be intimidated by it
Fast and intuitive interaction
User learning time is relatively short
Users get immediate feedback on their actions so mistakes can be quickly detected and corrected
Slide 21 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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The creation of an appropriate information space model (metaphor) for real world tasks and objects 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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 22

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Games
CAD systems
Files and Folders
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 23

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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
Slide 25 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 26

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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
Slide 27 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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Most general purpose systems
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 28

Title
NE W BOOK
ISBN
Author
Publisher
Edition
Classification
Date of purchase
Price
Publication date
Number of copies
Loan status
Order status
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 29

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Simple data entry
Easy to learn
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 30

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Takes up a lot of screen space
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 31

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Most systems involving significant data entry
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 32

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User types commands to give instructions to the system e.g. UNIX, DOS
Advantages:
• Powerful and flexible – good for experts
• Easy to process using compiler techniques
• Commands of arbitrary complexity can be created by command combination
• Concise interfaces requiring minimal typing can be created
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 33

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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
Slide 34 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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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
Slide 35 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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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
Slide 36 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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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
Slide 38 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

Information to be displayed
Presentation software
Display
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 39

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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
Slide 41 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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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?
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 42

Jan
2842
Feb
2851
Mar
3164
April
2789
May
1273
June
2835
4000
3000
2000
1000
0
Jan Feb Mar April May June
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 43

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 44

4
1
3
2
Dial with needle
0 10
Pie chart Thermometer Horizontal bar
20
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 45

0
Pressure
100 200 300 400 0 25
Temper atu re
50 75 100
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 46

!
The filename you have chosen h as been used. Please choose another name
Ch. 16 User interface design
OK Cancel
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 47

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Concerned with techniques for displaying large amounts of information
Visualisation can reveal relationships between entities and trends in the data
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 48

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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
Slide 49 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 50

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 51

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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
Slide 53 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

Context
Experience
Skill level
Style
Culture
©Ian Sommerville 2000
The user guidance system should be aware of what the user is doing and should adjust the output message to the current context.
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 system should provide both types of message and allow the user to control message conciseness.
Messages should be tailored to the user’s skills as well as their experience. Messages for the different classes of user may be expressed in different ways depending on the terminology which is familiar to the reader.
Messages should be positive rather than negative. They should use the active rather than the passive mode of address. They should never be insulting or try to be funny.
Wherever possible, the designer of messages should be familiar with the culture of the country where the system is sold. There are distinct cultural differences between Europe, Asia and
America. A suitable message for one culture unacceptable in another.
might be
Software Engineering, 6th edition. Chapter 15 Slide 54

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Context
Experience
Skill Level
Style
Culture
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 55

System and user-oriented error messages
System-oriented error message
?
OK
Error #27
Invalid patient id entered
Cancel
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 57

user-oriented error messages
User-oriented error message
Patient J . Bates is not registered
Click on Patients for a list of registered patients
Click on Retry to re-input a patient name
Click on Help for more information
Patients Help Retry Cancel
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 58

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 59

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 60

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 61

Top-level entry
Entry from application
Entry from error message system
©Ian Sommerville 2000
Help frame network
Software Engineering, 6th edition. Chapter 15 Slide 62

Help frame map
You are here
Help history
1. Mail
2. Send mail
3. Read mail
4. 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 more next top ics
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 63

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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
Slide 64 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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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
Slide 65 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

System evaluators
Functional description
Description of services
System administrators
Installation document
How to install the system
Novice users
Introductory manual
Getting started
Experienced users
Reference manual
Facility description
System administrators
Administrator’s guide
Operation and maintenance
Slide 66 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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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
Slide 68 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

Attribute
Learnability
Description
How long does it take a new user become productive with the system?
to
Speed of operation How well does the system response match the user’s work practice?
Robustness
Recoverability
How tolerant is the system of user error?
How good is the system at recovering from user errors?
Adaptability How closely is the system tied to a single model of work?
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 69

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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
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15
Galitz
Slide 70

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5 human factors central to community evaluation:
1. Time to learn
2. Speed of performance
3. Rate of errors by users
4. Retention over time
5. Subjective satisfaction
Trade-offs sometimes necessary
Test all design alternatives using mock-ups
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15
Galitz
Slide 71

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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
Galitz
Slide 72 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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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.
Slide 73 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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Guidelines review
Heuristic evaluation (will be covered last due to extensive coverage)
Cognitive walkthrough
Think aloud evaluations
Usability test
Classic experiments
Focus groups
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15
Galitz
Slide 74

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Scenarios
Simplified Thinking Aloud
Heuristic Evaluation
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15
Nielsen
Slide 75

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Take prototyping to extreme – reduce functionality AND number of features
Small, can afford to change frequently
Get quick and frequent feedback from users
Compatible with interface design methods
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15
Nielsen
Slide 76

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Bring in some users, give them tasks, have them think out loud
Fewer users in user testing
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15
Nielsen
Slide 77

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Context – part of iterative design
Goal – find usability problems
Who – small set of evaluators
How – study interface in detail, compare to small set of principles
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15
Nielsen
Slide 78

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More than one evaluator to be effective.
Each evaluator inspects the interface by themselves
General heuristics may be supplemented
Results can be oral or written
Evaluator spends 1-2 hours with interface
Evaluator goes through interface > 1 time
Evaluators may follow typical usage scenarios
Interface can be paper
Nielsen
Slide 79 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15

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State and the action alternatives should be visible
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Should be a good conceptual model with a consistent system image
Interface should include good mappings that reveal the relationships between stages
User should receive continuous feedback
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 82

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To follow … alphabetically (following book)
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 83

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Meaningful contrast between screen elements
Create groupings
Align screen elements and groups
Provide 3 dimensional representation
Use color and graphics effectively and simply
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 84

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Visual elements
Functions
Metaphors
Words and text
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 85

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With the user
With the task and job
With the product (past systems)
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 86

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User should easily be able to determine:
• What to look at
• What to do
• When to do it
• Where to do it
• Why to do it
• How to do it
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 87

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Users should be able to set preferences
Good Default Settings should be provided for non-tinkerers
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 88

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One of Shneiderman’s 8 golden rules for interface design
Similar components should
• Have similar look
• Operate similarly
Same action should always produce the same result
Function of elements should not change
Position of standard elements should not change
Same terminology used for same thing throughout
Standards and Guidelines increase the odds of consistency
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 89

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User should control the interaction
• Actions initiated by user
• Actions performed quickly
• Actions can be interrupted or stopped, and reversed
Context maintained is from the user’s perspective
More than one way to do things
Avoid modes
Configurable
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 90

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Provide Direct Manipulation
• user selects an object, then directly performs an action on it
• The effect of action on an object should be immediately visible
• Available alternatives reduces memory load
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 91

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Minimize eye and hand movements
• Make user actions flow from one to another
• Don’t switch users frequently from keyboard to mouse
Anticipate users wants and needs whenever possible
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 92

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Use language and concepts familiar to the user
Keep the interface natural
Use real world metaphors
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 93

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 compatible with the user’s “skills, experience, habits, and preferences, and current conditions”
Danger: more flexibility increases complexity of system
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 94

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Prevent errors from occurring when possible
Tolerate and forgive common and unavoidable human errors
When an error occurs, provide constructive error messages
Protect against catastrophic errors
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 95

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User should be able to anticipate the flow of the task
Expectations should be fulfilled
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 96

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System should permit:
• Commands or actions to be abolished or reversed
• Immediate return to a certain point if difficulties arise
Users should never lose work due to:
• An error on their part
• Hardware, software, or communication problems
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 97

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Respond rapidly to user requests
Provide acknowledgement of user actions
Beginners need more / more informative feedback than experts do
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 98

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Provide as simple an interface as possible
• Progressive disclosure
• Defaults
• Minimize screen alignment points
• Make common actions simple
• Provide consistency
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 99

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Allow user to focus on the task, not the interface
• Basic principle of direct manipulation
• Use user’s task vocabulary
• Design interface based on task analysis
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 100

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Final Design will always represent a series of trade-offs
People’s requirements always take precedence over technical requirements
©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 101