CS 501: Software Engineering Fall 2000AdministrationPowerPoint PresentationState Transition DiagramState Transition TableQuestion 4Slide 7Question 4Slide 9Slide 10Slide 11Distributed Objects and the System Life-CycleDesign for UsabilityIterative DesignMethods for Evaluation of UsabilityLevels of UsabilityThe Conceptual ModelInterface DesignPrinciples of Interface DesignDisabilitiesFunctional DesignSame Functions, Different InterfaceData and MetadataComputer Systems and NetworksDesign Tensions in Networked SystemsUsability and CostExtensibility in Web BrowsersCS 501: Software EngineeringFall 2000Lecture 17Design for Usability I2Administration• Midterm examination3Q2: Finite State MachineThe cruise control system on an automobile is controlled by a master switch and three buttons. Initially, it is turned on by the master switch. The master switch can be turned off at any time. When first turned on, the system enters stand-by mode. When the system is in stand-by mode, the driver of the automobile can press Button A to engage the cruise control at the current speed of the automobile. When the cruise control is engaged, if the driver presses the brake or presses Button B the system will be disengaged and return to stand-by mode. After returning to stand-by mode, the driver can press Button C to engage the cruise control at the speed that it was set at previously. (After the system is first turned on, Button C has no effect.) When the cruise control is engaged, the driver can press Button A to increase speed by one mile per hour or Button C to decrease speed by one mile per hour.4State Transition DiagramOff Standby Engaged Standby1MS-OnB-BrakeMS-OffAACCA5State Transition TableMSonMS offAB BrakeCOffStandbyEngagedStandby1StandbyOffOffOffEngagedStandby1EngagedEngagedEngagedEngaged6Question 4When software is written, who owns the copyright? How can somebody else be permitted to use the software? How can copyright be transferred to somebody else?7Question 4When software is written, who owns the copyright? The person who writes the softwareExcept work for hire -- the employerHow can somebody else be permitted to use the software? By permission from the copyright owner(usually a license)How can copyright be transferred to somebody else? Copyright is property that can be sold or given away(usually a contract)8Question 4 You are employed for company X writing software. When you leave, who owns your work? What use can you make of the work?9Question 4 You are employed for company X writing software. When you leave, who owns your work? The company (work for hire)What use can you make of the work? None without permission of the copyright owner10Question 4You work free-lance for company X. When you finish, who owns your work? What use can you make of the work?11Question 4You work free-lance for company X. When you finish, who owns your work? It depends on the circumstancesHave a written contractWhat use can you make of the work? If you hold the copyright -- unrestrictedOtherwise -- none without agreement12Distributed Objects and the System Life-CycleAll large systems change with time. • Dynamic binding of objects combined with polymorphism permits the addition of extra object types, incremental changes, etc. to be localized.Development environments change with time.• Language bindings and IIOP permit changes.Production environments changes with time.• Code can be reused in different environments.13Design for UsabilityUsability of a computer system is a combination of factors:• User interface design• Functionality• Performance• Help systems and documentation• Freedom from errorsAnything else?14Iterative DesignRequirementsDesignImplementation(prototype)Evaluation15Methods for Evaluation of Usability• Observing users (user protocols)• Focus groups• Measurements effectiveness in carrying out tasksspeed • Expert review• Client's opinions• Competitive analysis16Levels of Usabilityinterface designfunctional designdata and metadatacomputer systems and networksconceptual model17The Conceptual ModelThe conceptual model is the user's internal model of what the system provides:• The desk top metaphor -- files and folders• The web model -- click on hyperlinks• The library model -- search and retrieve• The form filling model -- fill form, submitExample: The Mercury page turner18Interface 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")Example: Screen space utilization in the Mercury page turner19Principles 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 offered shortcuts; beginners have simple, well-defined options The user should feel in control20Disabilities• What if the user:is visually impaired or color blind?does not speak English?is a poor typist? • There is a tradition of blind programmers• Navigation of web sites need not be only visualYou may have a legal requirement to support people with disabilities21Functional DesignThe functional design, determines the functions that are offered to the user • Selection of parts of a digital object• Searching a list or sorting the results• Help information• Manipulation of objects on a screen• Pan or zoom22Same Functions, Different InterfaceExample: The desk top metaphor• Mouse -- 1 button (Macintosh), 2 button (Windows) or 3 button (Unix)• Close button -- left of window (Macintosh) right of window (Windows)23Data and MetadataData and metadata stored by the computer system enable the functions and the interface• 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)• Data validation often requires that a user interface has access to a database (e.g., names and addresses)24Computer Systems and NetworksThe performance, reliability
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