User interface designObjectivesTopics coveredThe user interfaceHuman factors in interface designUI design principlesUser interface design principlesDesign principlesSlide 9Design issues in UIsInteraction stylesSlide 12Multiple user interfacesLIBSYS interactionWeb-based interfacesLIBSYS search formInformation presentationSlide 18Model-view-controllerSlide 20Information display factorsAlternative information presentationsAnalogue or digital presentation?Presentation methodsDisplaying relative valuesData visualisationColour displaysColour use guidelinesError messagesDesign factors in message wordingUser errorGood and bad message designThe UI design processThe design processUser analysisUser interaction scenarioRequirements from the scenarioAnalysis techniquesHierarchical task analysisInterviewingEthnographyEthnographic recordsInsights from ethnographyUser interface prototypingPaper prototypingPrototyping techniquesUser interface evaluationUsability attributesSimple evaluation techniquesKey pointsSlide 51©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 1User interface design©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 2ObjectivesTo suggest some general design principles for user interface designTo explain different interaction styles and their useTo explain when to use graphical and textual information presentationTo explain the principal activities in the user interface design processTo introduce usability attributes and approaches to system evaluation©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 3Topics coveredDesign issuesThe user interface design processUser analysisUser interface prototypingInterface evaluation©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 4The user interfaceUser interfaces should be designed to match the skills, experience and expectations of its anticipated users.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.©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 5Human factors in interface designLimited short-term memory•People can instantaneously remember about 7 items of information. If you present more than this, they are more liable to make mistakes.People make mistakes•When people make mistakes and systems go wrong, inappropriate alarms and messages can increase stress and hence the likelihood of more mistakes.People are different•People have a wide range of physical capabilities. Designers should not just design for their own capabilities.People have different interaction preferences•Some like pictures, some like text.©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 6UI 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.©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 7User interface design principlesPrincipleDescriptionUser familiarityThe interface should use terms and concepts which are drawnfrom the experience of the people who will make most use of thesystem.ConsistencyThe interface should be consistent in that, wherever possible,comparable operations should be activated in the same way.Minimal surpriseUsers should never be surprised by the behaviour of a system.RecoverabilityThe interface should include mechanisms to allow users torecover from errors.User guidanceThe interface should provide meaningful feedback when errorsoccur and provide context-sensitive user help facilities.User diversityThe interface should provide appropriate interaction facilities fordifferent types of system user.©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 8Design principles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 as letters, documents, folders etc. rather than directories, file identifiers, etc.Consistency•The system should display an appropriate level of consistency. Commands and menus should have the same format, command punctuation should be similar, etc.Minimal surprise•If a command operates in a known way, the user should be able to predict the operation of comparable commands©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 9Design principlesRecoverability•The system should provide some resilience to user errors and allow the user to recover from errors. This might include an undo facility, confirmation of destructive actions, 'soft' deletes, etc.User guidance•Some user guidance such as help systems, on-line manuals, etc. should be suppliedUser diversity•Interaction facilities for different types of user should be supported. For example, some users have seeing difficulties and so larger text should be available©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 10Design issues in UIsTwo problems must be addressed in interactive systems design•How should information from the user be provided to the computer system?•How should information from the computer system be presented to the user?User interaction and information presentation may be integrated through a coherent framework such as a user interface metaphor.©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 11Interaction stylesDirect manipulationMenu selectionForm fill-inCommand languageNatural language©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 16 Slide 12Interaction stylesInteractionstyleMain advantagesMain disadvantagesApplicationexamplesDirectmanipulationFast and intuitiveinteractionEasy to learnMay be hard to implement.Only suitable where there is avisual metaphor for tasks andobjects.Video