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

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

User interface design

Designing effective interfaces for software systems


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 Software engineers generally must do interface

design


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

Galitz


Benefits of Good Design 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.

Galitz


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

•Windows

•Icons

•Menus

•Pointing

•Graphics


GUI advantages 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


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

Executableprototype

Designprototype

Produce paper-based design

prototype

Producedynamic design

prototype

Evaluate designwith end-users

Implementfinal userinterface

Evaluate designwith end-users

Analyse andunderstand user

activities


15.1 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 principlesPrinciple 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 Users should be able to recover from their errors

User Guidance Meaningful feedback, context-sensitive help

User Diversity Should provide for different types of user


Nielsen’s Ten Usability Heuristics 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


Galitz’s Heuristics (Table 14.2)1. Automate unwanted workload2. Reduce uncertainty3. Fuse data4. Present new info with meaningful aid to interpretation5. Use names that are conceptually related to functions6. Group data in consistently meaningful ways to reduce

search time7. Limit data-driven tasks8. Include in displays only info needed by user at a given

time9. Provide multiple coding of data where appropriate10. Practice judicious redundancy Galitz


Galitz’s WWW Heuristics1. Speak the user’s language

2. Be consistent

3. Minimize the user’s memory load

4. Build flexible and efficient systems

5. Design aesthetic and minimalist systems

6. Use chunking

7. Provide progressive levels of detail

8. Give navigational feedback

9. Don’t lie to the user

Galitz


15.2 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


Direct manipulation advantages 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


Direct manipulation problems 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


Direct Manipulation Applications Games CAD systems Files and Folders


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


Menu System Applications Most general purpose systems


Form-based interface

Title

Author

Publisher

Edition

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Date ofpurchase

ISBN

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Publicationdate

Number ofcopies

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NEW BOOK


Forms-based Systems Advantages Simple data entry Easy to learn


Forms-based Systems Disadvantages Takes up a lot of screen space


Forms-based Systems Applications Most systems involving significant data entry


Command interfaces

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


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


15.3 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 tobe displayed

Presentationsoftware

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

0

1000

2000

3000

4000

Jan Feb Mar April May June

Jan2842

Feb2851

Mar3164

April2789

May1273

June2835


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 20 10 20

Dial with needle Pie chart Thermometer Horizontal bar


Displaying relative values

0 100 200 300 400 0 25 50 75 100

Pressure Temperature


Textual highlighting

The filename you have chosen has beenused. 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


15.3.1 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


15.4 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


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 wordingContext The user guidance system should be aware of what the user is

doing and should adjust the output message to the currentcontext.

Experience As users become familiar with a system they become irritatedby long, ‘meaningful’ messages. However, beginners find itdifficult to understand short terse statements of the problem.The user guidance system should provide both types of messageand allow the user to control message conciseness.

Skill level Messages should be tailored to the user’s skills as well as theirexperience. Messages for the different classes of user may beexpressed in different ways depending on the terminology whichis familiar to the reader.

Style Messages should be positive rather than negative. They shoulduse the active rather than the passive mode of address. Theyshould never be insulting or try to be funny.

Culture Wherever possible, the designer of messages should be familiarwith the culture of the country where the system is sold. Thereare distinct cultural differences between Europe, Asia andAmerica. A suitable message for one culture might beunacceptable in another.


Design factors in message wording Context Experience Skill Level Style Culture


System and user-oriented error messages

Error #27

Invalid patient id entered?OK Cancel

System-oriented error message


user-oriented error messages

Patient J . Bates is not registered

Click on Patients for a list of registered patientsClick on Retry to re-input a patient nameClick on Help for more inf ormation

Patients Help Retry Cancel

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 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

Help frame network

Top-levelentry

Entry from errormessage system

Entry fromapplication


Help system windows

Mail redirection

Mail may be redirected to anothernetwork user by pressing theredirect button in the controlpanel. The system asks for thename of the user or users towhom the mail has been sent

next topicsmore

Mail redirection

Mail may be redirected to anothernetwork user by pressing theredirect button in the controlpanel. The system asks for thename of the user or users towhom the mail has been sent

Help frame map

You are here

Help history

1. Mail2. Send mail3. Read mail4. 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


5.4.3 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 ofservices

Functionaldescription

Systemevaluators

How to installthe system

Installationdocument

Systemadministrators

Gettingstarted

Introductorymanual

Noviceusers

Facilitydescription

Referencemanual

Experiencedusers

Operation andmaintenance

Administrator’sguide

Systemadministrators


15.5 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 DescriptionLearnability How long does 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 system of user error?Recoverability How good is the system at recovering from

user errors?Adaptability How closely is the system tied to a single

model of work?


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 Galitz


…System - User Interface Design Goals 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

Galitz


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

Galitz


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

Galitz


Elements of Discount Usability Engineering

Scenarios Simplified Thinking Aloud Heuristic Evaluation

Nielsen


Scenarios 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

Nielsen


Simplified Thinking Aloud Bring in some users, give them tasks, have them

think out loud Fewer users in user testing

Nielsen


Heuristic Evaluation

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

Nielsen


How to Conduct a Heuristic Evaluation

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


Norman’s Four Principles of Good Design

State and the action alternatives should be visible 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


Galitz’s Principles of User Interface Design

To follow … alphabetically (following book)


Aesthetically Pleasing Meaningful contrast between screen elements Create groupings Align screen elements and groups Provide 3 dimensional representation Use color and graphics effectively and simply


Clarity Visual elements Functions Metaphors Words and text


Compatible With the user With the task and job With the product (past systems)


Comprehensibility 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


Configurability Users should be able to set preferences Good Default Settings should be provided for

non-tinkerers


Consistency 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


Control 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


Directness 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


Efficiency 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


Familiarity

Use language and concepts familiar to the user Keep the interface natural Use real world metaphors


Flexibility compatible with the user’s “skills, experience,

habits, and preferences, and current conditions” Danger: more flexibility increases complexity of

system


Forgiveness 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


Predictability User should be able to anticipate the flow of the

task Expectations should be fulfilled


Recovery 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


Responsiveness Respond rapidly to user requests Provide acknowledgement of user actions Beginners need more / more informative feedback

than experts do


Simplicity Provide as simple an interface as possible

• Progressive disclosure

• Defaults

• Minimize screen alignment points

• Make common actions simple

• Provide consistency


Transparency 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


Trade-offs Final Design will always represent a series of

trade-offs People’s requirements always take precedence

over technical requirements

Documents

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