ui principles

8/15/2019 UI Principles

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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 1

User interface design


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Objectives

q To suggest some general design principles for user interface design

q To explain different interaction styles and their useq

To explain when to use graphical and textualinformation presentation

q To explain the principal activities in the user interface design process

q To introduce usability attributes and approaches tosystem evaluation


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Topics covered

q Design issuesq The user interface design processq User analysisq User interface prototypingq Interface evaluation


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The user interface

q User interfaces should be designed to matchthe skills, experience and expectations of itsanticipated users.

q

System users often judge a system by itsinterface rather than its functionality.q A poorly designed interface can cause a user

to make catastrophic errors.q Poor user interface design is the reason why

so many software systems are never used.


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Human factors in interface design

q Limited short-term memory People can instantaneously remember about 7 items of

information. If you present more than this, they are moreliable to make mistakes.

q

People make mistakes When people make mistakes and systems go wrong,

inappropriate alarms and messages can increase stressand hence the likelihood of more mistakes.

q People are different People have a wide range of physical capabilities.

Designers should not just design for their owncapabilities.

q People have different interaction preferences Some like pictures, some like text.


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UI design principles

q UI design must take account of the needs,experience and capabilities of the systemusers.

q

Designers should be aware of peoplesphysical and mental limitations (e.g. limitedshort-term memory) and should recognisethat people make mistakes.

q

UI design principles underlie interfacedesigns although not all principles areapplicable to all designs.


7/51 Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 7

User interface design principles

Principle Description

User familiarity The interface should use terms and concepts which are drawnfrom the experience of the people who will make most use of thesystem.

Consistency The interface should be consistent in that, wherever possible,comparable operations should be activated in the same way.

Minimal surprise Users should never be surprised by the behaviour of a system.

Recoverability The interface should include mechanisms to allow users torecover from errors.

User guidance The interface should provide meaningful feedback when errorsoccur and provide context-sensitive user help facilities.

User diversity The interface should provide appropriate interaction facilities for different types of system user.



Design principles

q 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 asletters, documents, folders etc. rather than directories, fileidentifiers, etc.

q Consistency The system should display an appropriate level

of consistency. Commands and menus should have thesame format, command punctuation should be similar,etc.

q Minimal surprise If a command operates in a known way, the user should

beable to predict the operation of comparable commands



Design principles

q Recoverability The system should provide some resilience to

user errors and allow the user to recover from errors. Thismight include an undo facility, confirmation of destructiveactions, 'soft' deletes, etc.

q User guidance Some user guidance such as help systems, on-line

manuals, etc. should be suppliedq User diversity

Interaction facilities for different types of user should besupported. For example, some users have seeingdifficulties and so larger text should be available



Design issues in UIs

q Two problems must be addressed in interactivesystems design

How should information from the user be provided to thecomputer system?

How should information from the computer system bepresented to the user?

q User interaction and information presentation maybe integrated through a coherent framework such as

a user interface metaphor.



Interaction styles

q Direct manipulationq Menu selectionq Form fill-inq Command languageq Natural language



Interaction styles

Interactionstyle

Main advantages Main disadvantages Applicationexamples

Directmanipulation

Fast and intuitiveinteractionEasy to learn

May be hard to implement.Only suitable where there is avisual metaphor for tasks andobjects.

Video gamesCAD systems

Menuselection

Avoids user errorLittle typing required

Slow for experienced users.Can become complex if manymenu options.

Most general-purpose systems

Form fill-in Simple data entryEasy to learnCheckable

Takes up a lot of screen space.Causes problems where useroptions do not match the formfields.

Stock control,Personal loanprocessing

Commandlanguage

Powerful and flexible Hard to learn.Poor error management.

Operating systems,Command andcontrol systems

Naturallanguage

Accessible to casualusersEasily extended

Requires more typing.Natural language understandingsystems are unreliable.

Informationretrieval systems



Multiple user interfaces

Linux operating system

X-windows GUImanager

Graphical userinterface

(Gnome/KDE)

Commandlanguage

interpreter

Unix shellinterface(ksh/csh)



LIBSYS interaction

q Document search Users need to be able to use the search

facilities to find the documents that they need.q Document request

Users request that a document be delivered totheir machine or to a server for printing.


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Web-based interfaces

q Many web-based systems have interfacesbased on web forms.

q Form field can be menus, free text input,radio buttons, etc.

q In the LIBSYS example, users make achoice of where to search from a menu and

type the search phrase into a free text field.


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LIBSYS search form

LIBSYS: Search

Choose collection

Keyword or phrase

Search using

Adjacent words

Search Reset Cancel

All

Title

Yes No


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Information presentation

q Information presentation is concerned withpresenting system information to systemusers.

q

The information may be presented directly(e.g. text in a word processor) or may betransformed in some way for presentation(e.g. in some graphical form).

q

The Model-View-Controller approach is away of supporting multiple presentations of data.


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Information tobe displayed

Presentationsoftware

Display


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Model-view-controller

Model methods

Controller methods View methods

Userinputs

view modificationmessages

Model edits

Model queriesand updates

Controller state View state

Model state


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q Static information Initialised at the beginning of a session. It does

not change during the session.

May be either numeric or textual.q Dynamic information

Changes during a session and the changesmust be communicated to the system user.

May be either numeric or textual.


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Information display factors

q Is the user interested in precise information or data relationships?

q How quickly do information values change?

Must the change be indicated immediately?q Must the user take some action in response toa change?

q Is there a direct manipulation interface?q

Is the information textual or numeric? Are relativevalues important?


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Alternative information presentations

0

1000

2000

3000

4000

Jan Feb Mar April May June

Jan2842

Feb2851

Mar3164

April2789

May1273

June2835


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Analogue or digital presentation?q Digital presentation

Compact - takes up little screen space; Precise values can be communicated.

q 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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Presentation methods

1

3

4 2 0 10 20

Dial with needle Pie chart Thermometer Horizontal bar


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Displaying relative values

0 100 200 300 400 0 25 50 75 100Pressure Temperature


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Data visualisation

q Concerned with techniques for displaying largeamounts of information.

q Visualisation can reveal relationships betweenentities and trends in the data.

q 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.


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Colour displays

q Colour adds an extra dimension to aninterface and can help the user understandcomplex information structures.

q Colour can be used to highlight exceptionalevents.

q Common mistakes in the use of colour in

interface design include: The use of colour to communicate meaning; The over-use of colour in the display.


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Colour use guidelines

q Limit the number of colours used and beconservative in their use.

q Use colour change to show a change in

system status.q Use colour coding to support the task that

users are trying to perform.q Use colour coding in a thoughtful and

consistent way.q Be careful about colour pairings.


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Error messages

q Error message design is critically important.Poor error messages can mean that a user rejects rather than accepts a system.

q Messages should be polite, concise,consistent and constructive.

q The background and experience of users

should be the determining factor in messagedesign.


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Design factors in message wording

Factor Description

Context Wherever possible, the messages generated by the system should reflect the currentuser context. As far as is possible, the system should be aware of what the user is doingand should generate messages that are relevant to their current activity.

Experience As u sers become familiar with a s ystem they become irritated by long, meaningfulmessages. However, beginners find it difficult to understand short terse statements of a problem. You should provide both types of message and allow the user to controlmessage conciseness.

Skill level Messages should be tailored to the usersskills as well as their experience. Messagesfor the different classes of user may be expressed in different ways depending on theterminology that is familiar to the reader.

Style 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.

Culture Wherever possible, the designer of messages should be familiar with the culture of thecountry where the system is sold. There are distinct cultural differences betweenEurope, Asia and America. A su itable message for one culture might be unacceptablein another.


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User error

q Assume that a nurse misspells the name of apatient whose records he is trying to retrieve.

Please type the patients name in the bo x then click on OK

MacDonald, R.

OK Cancel

Patients name


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Good and bad message design

Error #27

Invalid patient id

OK Cancel

System-oriented error message User-oriented error message

R. MacDonald is not a reg ist ered patientClick on Patients f or a list of patientsClick on Retr y to re-input the patients nameClick on Help f or more inf ormation

Patients Help Retry Cancel


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The UI design process

q UI design is an iterative process involvingclose liaisons between users and designers.

q The 3 core activities in this process are:

User analysis . Understand what the users willdo with the system; System prototyping . Develop a series of

prototypes for experiment; Interface evaluation . Experiment with these

prototypes with users.


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The 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


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User analysis

q If you dont understand what the users wantto do with a system, you have no realisticprospect of designing an effective interface.

q User analyses have to be described in termsthat users and other designers canunderstand.

q

Scenarios where you describe typicalepisodes of use, are one way of describingthese analyses.


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User interaction scenario

Jane is a student of Religious Studies and is working on an essayon Indian architecture and how it has been influenced by religiouspractices. To help her understand this, she would like to access

some pictures of details on notable buildings but cant findanything in her local library.

She approaches the subject librarian to discuss her needs and hesuggests some search terms that might be used. He also suggestssome libraries in New Delhi and London that might have this

material so they log on to the library catalogues and do somesearching using these terms. They find some source material andplace a request for photocopies of the pictures with architecturaldetail to be posted directly to Jane.


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Requirements from the scenario

q Users may not be aware of appropriatesearch terms so need a way of helping themchoose terms.

q Users have to be able to select collections tosearch.

q Users need to be able to carry out searches

and request copies of relevant material.


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Analysis techniques

q Task analysis Models the steps involved in completing a task.

q Interviewing and questionnaires Asks the users about the work they do.

q Ethnography Observes the user at work.


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Hierarchical task analysis

Retrieve picturesfrom remote

libraries

Discover

possiblesources

Establish

searchterms

S earch forpictures

Request

photocopiesof found ite ms

1 2 3 4.

Se lec tlibrary

Log in tocatalogue

S earch forpictures

Modify

search terms

Recordrelevant

items

3.1 3.2 3.3 3.4 3.5

Enter searchterms

Initiatesearch

Reviewresults

3.3.1 3.3.2 3.3.3

do 1, 2,3 until pic tures found, 4

do 3.1, 3.2,3.3 until pictures found,3.4 if necessary, 3.5

do 3.3.1, 3.3.2, 3.3.3


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Interviewing

q Design semi-structured interviews based onopen-ended questions.

q Users can then provide information that theythink is essential; not just information thatyou have thought of collecting.

q Group interviews or focus groups allow usersto discuss with each other what they do.


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Ethnography

q Involves an external observer watchingusers at work and questioning them in anunscripted way about their work.

q Valuable because many user tasks areintuitive and they find these very difficult todescribe and explain.

q Also helps understand the role of social andorganisational influences on work.


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Ethnographic records

Air traffic control involves a number of control suites where the suitescontrolling adjacent sectors of airspace are physically located next toeach other. Flights in a sector are represented by paper strips that arefitted into wooden racks in an order that reflects their position in thesector. If there are not enough slots in the rack (i.e. when the airspaceis very busy), controllers spread the strips out on the desk in front of therack.

When we were observing controllers, we noticed that controllersregularly glanced at the strip racks in the adjacent sector. We pointed

this out to them and asked them why they did this. They replied that, if the adjacent controller has strips on their desk, then this meant that theywould have a lot of flights entering their sector. They therefore tried toincrease the speed of aircraft in the sector to clear space for theincoming aircraft.


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Insights from ethnography

q Controllers had to see all flights in a sector.Therefore, scrolling displays where flightsdisappeared off the top or bottom of the

display should be avoided.q The interface had to have some way of

telling controllers how many flights were inadjacent sectors so that they could plan their workload.


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User interface prototyping

q The aim of prototyping is to allow users togain direct experience with the interface.

q Without such direct experience, it is

impossible to judge the usability of aninterface.q Prototyping may be a two-stage process:

Early in the process, paper prototypes may be

used; The design is then refined and increasinglysophisticated automated prototypes are thendeveloped.


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Paper prototyping

q Work through scenarios using sketches of the interface.

q Use a storyboard to present a series of interactions with the system.

q Paper prototyping is an effective way of getting user reactions to a design proposal.


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Prototyping techniques

q Script-driven prototyping Develop a set of scripts and screens using a

tool such as Macromedia Director. When theuser interacts with these, the screen changes tothe next display.

q Visual programming Use a language designed for rapid development

such as Visual Basic. See Chapter 17.q Internet-based prototyping

Use a web browser and associated scripts.


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User interface evaluation

q Some evaluation of a user interface designshould be carried out to assess its suitability.

q Full scale evaluation is very expensive and

impractical for most systems.q Ideally, an interface should be evaluated

against a usability specification. However, itis rare for such specifications to beproduced.


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Usability attributes


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Simple evaluation techniques

q Questionnaires for user feedback.q Video recording of system use and

subsequent tape evaluation.q Instrumentation of code to collect information

about facility use and user errors.q The provision of code in the software to

collect on-line user feedback.


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Key points

q User interface design principles should help guidethe design of user interfaces.

q Interaction styles include direct manipulation, menusystems form fill-in, command languages andnatural language.

q Graphical displays should be used to present trendsand approximate values. Digital displays whenprecision is required.

q Colour should be used sparingly and consistently.


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Key points

q The user interface design process involves user analysis, system prototyping and prototypeevaluation.

q The aim of user analysis is to sensitise designers to

the ways in which users actually work.q UI prototyping should be a staged process with early

paper prototypes used as a basis for automatedprototypes of the interface.

q The goals of UI evaluation are to obtain feedback onhow to improve the interface design and to assess if the interface meets its usability requirements.

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