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User interface design - PowerPoint PPT Presentation

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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

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User interface design l.jpg
User interface design

  • Designing effective interfaces for software systems

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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

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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


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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.


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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

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GUI characteristics

  • Windows

  • Icons

  • Menus

  • Pointing

  • Graphics

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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

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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

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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

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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


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Galitz’s Heuristics (Table 14.2)

  • 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


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Galitz’s WWW Heuristics

  • 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


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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

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Interaction styles

  • Direct manipulation

  • Menu selection

  • Form fill-in

  • Command language

  • Natural language

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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

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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

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Direct Manipulation Applications

  • Games

  • CAD systems

  • Files and Folders

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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

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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

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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

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Menu System Applications

  • Most general purpose systems

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Forms-based Systems Advantages

  • Simple data entry

  • Easy to learn

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Forms-based Systems Disadvantages

  • Takes up a lot of screen space

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Forms-based Systems Applications

  • Most systems involving significant data entry

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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

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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

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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

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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

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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

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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

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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?

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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

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Data visualisation

  • Concerned with techniques for displaying large amounts of information

  • Visualisation can reveal relationships between entities and trends in the data

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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

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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

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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

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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

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Design factors in message wording

  • Context

  • Experience

  • Skill Level

  • Style

  • Culture

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System and user-oriented error messages

System-oriented error message



or #27



alid patient id entered



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user-oriented error messages

User-oriented error message


atient J


Bates is not registered


k on P

atients f

or a list of registered patients


k on Retr

y to re-input a patient name


k on Help f

or more inf









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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

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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

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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

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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

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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

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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

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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


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…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


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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


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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.

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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


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Elements of Discount Usability Engineering

  • Scenarios

  • Simplified Thinking Aloud

  • Heuristic Evaluation


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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


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Simplified Thinking Aloud

  • Bring in some users, give them tasks, have them think out loud

  • Fewer users in user testing


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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


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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


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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

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Galitz’s Principles of User Interface Design

  • To follow … alphabetically (following book)

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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

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  • Visual elements

  • Functions

  • Metaphors

  • Words and text

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  • With the user

  • With the task and job

  • With the product (past systems)

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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

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  • Users should be able to set preferences

  • Good Default Settings should be provided for non-tinkerers

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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

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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

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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

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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

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  • Use language and concepts familiar to the user

  • Keep the interface natural

  • Use real world metaphors

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  • compatible with the user’s “skills, experience, habits, and preferences, and current conditions”

  • Danger: more flexibility increases complexity of system

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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

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  • User should be able to anticipate the flow of the task

  • Expectations should be fulfilled

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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

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  • Respond rapidly to user requests

  • Provide acknowledgement of user actions

  • Beginners need more / more informative feedback than experts do

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  • Provide as simple an interface as possible

    • Progressive disclosure

    • Defaults

    • Minimize screen alignment points

    • Make common actions simple

    • Provide consistency

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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

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  • Final Design will always represent a series of trade-offs

  • People’s requirements always take precedence over technical requirements