CS 501: Software EngineeringCourse AdministrationPresentationsDesignSoftware DesignLectures on DesignUsability: ReadingUsability: The Design/Evaluate LoopDesign for UsabilityDesign from a System ViewpointMental ModelSlide 12Interface DesignPrinciples of Interface DesignFunctional DesignData and metadataComputer systems and networksNon-functional RequirementsStyle of User Interfaces: Command Line InterfacesStyle of User Interfaces: Direct InteractionDesign for Direct ManipulationDesign for Direct Manipulation: MenusHelp System DesignInformation PresentationInformation Presentation: Separation of Presentation from ContentSystem Considerations of User InterfacesEvaluationSlide 28Evaluation without UsersMeasurementEvaluation based on MeasurementsEvaluation with UsersEvaluation with Users PreparationUsability LaboratoryEvaluation with Users Sessions ConductEvaluation with Users Results AnalysisEvaluation Example: Eye TrackingPowerPoint PresentationRefining the design based on evaluationThe Importance of User Interface DesignUser Interface Design1990Slide 432003Slide 45Slide 462006Slide 48Slide 49Slide 50Slide 511CS 501 Spring 2006CS 501: Software EngineeringLectures 11 & 12Usability2CS 501 Spring 2006Course AdministrationQuiz 2 on Thursday Same format as the first quizQuiz 3 will be on March 163CS 501 Spring 2006PresentationsProject PresentationsFirst presentation is next week, Tuesday through Thursday.Meeting room is at 301 College Avenue.For instructions, read the Assignments page.Schedule your presentation now!!!!Available time slots are on the Home page.Your client must attend the presentation unless you have special permission.4CS 501 Spring 2006DesignRequirementsOperation andMaintenanceImplementationDesignFeasibility andPlanningYour understand the requirements, now to design the system.5CS 501 Spring 2006Software DesignThe design phase is the most creative part of software development.The design must:• Meet the requirements • Satisfy the users• Provide flexibility for changing requirements• Be suitable for implementation with available resources• Be testable and maintainable• Fit within the style of the organization(s)6CS 501 Spring 2006Lectures on DesignLectures Topic11-12 Usability13-14 System Architecture15-18 Object Oriented Design7CS 501 Spring 2006Usability: ReadingReading: Mitchell Kapor, A Software Design Manifesto. Dr. Dobbs Journal, 1991. http://hci.stanford.edu/bds/1-kapor.html"Software design is not the same as user interface design.""Architects, not construction engineers, are the professionals who have overall responsibility for creating buildings. ... in the actual process of designing and implementing the building, the engineers take direction from the architects."8CS 501 Spring 2006Usability: The Design/Evaluate LoopEvaluate?DesignBuildAnalyze requirements9CS 501 Spring 2006Design for UsabilityUsability of a computer system is a combination of factors:• User interface design• Functionality• Performance• Help systems and documentation• Freedom from errorsAnything else?10CS 501 Spring 2006Design from a System Viewpointinterface designfunctional designdata and metadatacomputer systems and networksmentalmodel11CS 501 Spring 2006Mental ModelThe mental (conceptual) model is the user's internal model of what the system provides:• The desk top metaphor -- files and folders• The Web model -- pages with hyperlinks12CS 501 Spring 2006Mental ModelWhat a person thinks is true about a system, not necessarily what is actually true•Similar in structure to the system that is represented•Allows a person to predict the results of his actions•Simpler than the represented system. A mental model includes only enough information to allow accurate predictions (i.e. no data structures)Also called conceptual model13CS 501 Spring 2006Interface DesignThe interface design is the appearance on the screen and the actual manipulation by the user • Fonts, colors, logos, key board controls, menus, buttons• Mouse control or keyboard control?• Conventions (e.g., "back", "help")Examples: • Screen space utilization in Acrobat.• Number of snippets per page in Web search.14CS 501 Spring 2006Principles of Interface DesignInterface design is partly an art; there are general principles: • Consistency -- in appearance, controls, and function. • Feedback -- what is the computer system is doing? why does the user see certain results? • Users should be able to interrupt or reverse actions • Error handling should be simple and easy to comprehend • Skilled users should be offered shortcuts; beginners should have simple, well-defined options The user should feel in control15CS 501 Spring 2006Functional DesignThe functional design, determines the functions that are offered to the user • Selection of parts of an object• Searching a list or sorting the results• Help information• Manipulation of objects on a screen• Pan or zoomThere may be many user interface choices for the same function, e.g., Macintosh v. Windows desktop16CS 501 Spring 2006Data and metadataStructural data and metadata stored by the computer system enable the functions and the interface• Effectiveness of searching depends on the type and quality of data that is indexed (free-text, controlled vocabulary, etc.)• The desktop metaphor has the concept of associating a file with an application. This requires a file type to be stored with each file: -- extension to filename (Windows and Unix) -- resource fork (Macintosh)17CS 501 Spring 2006Computer systems and networksThe performance, reliability and predictability of computer systems and networks is crucial to usability18CS 501 Spring 2006Non-functional RequirementsPerformance, Reliability, Scalability, Security…Example: Response time0.1 sec – the user feels that the system is reacting instantaneously1 sec – the user will notice the delay, but his/her flow of thought stays uninterrupted10 sec – the limit for keeping the user's attention focused on the dialogue19CS 501 Spring 2006Style of User Interfaces:Command Line InterfacesUser interacts with computer by typing commands• Allows complex instructions to be given to computer• Facilitates formal methods of specification & implementation• Skilled users can input commands quickly• Requires learning or training• Can be adapted for people with disabilities• Can be
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