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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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 2
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 3
Topics covered
q Design issuesq The user interface design processq User analysisq User interface prototypingq Interface evaluation
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 4
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 5
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 6
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.
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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.
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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
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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
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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.
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Interaction styles
q Direct manipulationq Menu selectionq Form fill-inq Command languageq Natural language
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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
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Multiple user interfaces
Linux operating system
X-windows GUImanager
Graphical userinterface
(Gnome/KDE)
Commandlanguage
interpreter
Unix shellinterface(ksh/csh)
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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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 15
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 16
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 17
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 18
Information presentation
Information tobe displayed
Presentationsoftware
Display
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 19
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 20
Information presentation
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 21
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 22
Alternative information presentations
0
1000
2000
3000
4000
Jan Feb Mar April May June
Jan2842
Feb2851
Mar3164
April2789
May1273
June2835
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 23
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 24
Presentation methods
1
3
4 2 0 10 20
Dial with needle Pie chart Thermometer Horizontal bar
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 25
Displaying relative values
0 100 200 300 400 0 25 50 75 100Pressure Temperature
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 26
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 27
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 28
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 29
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 30
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 31
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 32
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 33
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 34
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 35
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 36
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 37
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 38
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 39
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 40
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 41
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 42
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 43
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 44
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 45
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 46
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 47
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 48
Usability attributes
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 49
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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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 50
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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