ch15.ppt User Interfaces

1 Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 1 user interface design Designing effective interfacesfor software systems Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 2 Objectives To suggest some general design principles foruser interface design To explain different interaction styles To introduce styles of information presentation To describe the user support which should bebuilt-in to user Interfaces To introduce usability attributes and systemapproaches to system evaluation Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 3 Topics covered user interface design principles user interaction Information presentation user support interface evaluation Ian Sommerville 2000 Software Engineering, 6th edition.

2 Chapter 15 Slide 4 The user interface System users often judge a system by itsinterface rather than its functionality A poorly designed interface can cause a user tomake catastrophic errors Poor user interface design is the reason why somany software systems are never used Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 5 Graphical user Interfaces Most users of business systems interact with thesesystems through graphical Interfaces although, insome cases, legacy text-based Interfaces are stillused Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 6 GUI characteristicsCharacteristicDescription WindowsMultiple windows allow different information to bedisplayed simultaneously on the user s different types of information.

3 On some systems,icons represent files; on others, icons are selected from a menu rather than typedin a command pointing device such as a mouse is used for selectingchoices from a menu or indicating items of interest in elements can be mixed with text on the samedisplay. Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 7 GUI advantages They are easy to learn and use. Users without experience can learn to use the systemquickly. The user may switch quickly from one task toanother and can interact with several differentapplications. Information remains visible in its own window whenattention is switched.

4 Fast, full-screen interaction is possible withimmediate access to anywhere on the screen Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 8 user -centred design The aim of this chapter is to sensitise softwareengineers to key issues underlying the designrather than the implementation of user Interfaces user -centred design is an approach to UI designwhere the needs of the user are paramount andwhere the user is involved in the design process UI design always involves the development ofprototype Interfaces Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 9 user interface design processExecutableprototypeDesignprototyp eProduce paper-based designprototypeProducedynamic designprototypeEvaluate designwith end-usersImplementfinal userinterfaceEvaluate designwith end-usersAnalyse andunderstand useractivities Ian Sommerville 2000 Software Engineering, 6th edition.

5 Chapter 15 Slide 10UI design principles UI design must take account of the needs,experience and capabilities of the system users Designers should be aware of people s physicaland mental limitations ( limited short-termmemory) and should recognise that people makemistakes UI design principles underlie interface designsalthough not all principles are applicable to alldesigns Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 11 user interface design principlesPrincipleDescriptionUser familiarityThe interface should use terms and concepts which aredrawn from the experience of the people who willmake most use of the interface should be consistent in that, whereverpossible.

6 Comparable operations should be activated inthe same surpriseUsers should never be surprised by the behaviour of interface should include mechanisms to allowusers to recover from guidanceThe interface should provide meaningful feedbackwhen errors occur and provide context-sensitive userhelp diversityThe interface should provide appropriate interactionfacilities for different types of system user . Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 12 Design principles user familiarity The interface should be based on user -orientedterms and concepts rather than computer concepts.

7 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 levelof consistency. Commands and menus should have the sameformat, command punctuation should be similar, etc. Minimal surprise If a command operates in a known way, the user should beable to predict the operation of comparable commands Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 13 Design principles Recoverability The system should provide some resilience touser errors and allow the user to recover from errors.

8 This mightinclude an undo facility, confirmation of destructive actions,'soft' deletes, etc. user guidance Some user guidance such as help systems, on-line manuals, be supplied user diversity Interaction facilities for different types of user should besupported. For example, some users have seeing difficulties andso larger text should be available Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 14 user -system interaction 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 be presentedto the user ?

9 user interaction and information presentationmay be integrated through a coherent frameworksuch as a user interface metaphor Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 15 Interaction styles Direct manipulation Menu selection Form fill-in Command language Natural languageAdvantages anddisadvantagesInteractionstyleMainadva ntagesMaindisadvantagesApplicationexampl esDirectmanipulationFast and intuitiveinteractionEasy to learnMay be hard toimplementOnly suitable wherethere is a visualmetaphor for tasksand objectsVideo gamesCAD systemsMenuselectionAvoids usererrorLittle typingrequiredSlow forexperienced usersCan becomecomplex if manymenu optionsMost general-purpose systemsForm fill-inSimple dataentryEasy to learnTakes up a lot ofscreen spaceStock control.

10 Personal loanprocessingCommandlanguagePowerful andflexibleHard to learnPoor errormanagementOperating systems,Libraryinformationretrieval systemsNaturallanguageAccessible tocasual usersEasily extendedRequires moretypingNatural languageunderstandingsystems areunreliableTimetable systemsWWWinformationretrieval systems Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 15 Slide 17 Direct manipulation advantages Users feel in control of the computer and are lesslikely to be intimidated by it user learning time is relatively short Users get immediate feedback on their actionsso mistakes can be quickly detected andcorrected Ian Sommerville 2000 Software Engineering, 6th edition.