CS 501: Software EngineeringAdministrationDesign for UsabilityElements of an InterfaceLevels of UsabilityThe Conceptual ModelInterface DesignPrinciples of Interface DesignDisabilitiesFunctional DesignSame Functions, Different InterfaceData and MetadataComputer Systems and NetworksDesign Tensions in Networked SystemsUsability and CostUsability: Requirements and RefinementUser Interfaces: Iterative DesignMethods for Specifying Requirements and Evaluation of Usability1CS 501 Spring 2002CS 501: Software EngineeringLecture 11Designing for Usability I2CS 501 Spring 2002AdministrationRequirements Presentation next weekSign up with Rosemary Adessa for a time.3CS 501 Spring 2002Design for UsabilityUsability of a computer system is a combination of factors:• User interface design• Functionality• Performance• Help systems and documentation• Freedom from errorsAnything else?4CS 501 Spring 2002Elements of an Interfacemetaphors: terms, images, concepts that can be learnedmental model: organization and representation of data, functions, tasks and rolesnavigation rules: how to move among data functions, activities and roleslook: characteristics of the appearance that convey informationfeel: interaction techniques that provide an appealing experienceMarcus (1993) quoted by Pfleeger5CS 501 Spring 2002Levels of Usabilityinterface designfunctional designdata and metadatacomputer systems and networksconceptual model6CS 501 Spring 2002The 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 turner7CS 501 Spring 2002Interface DesignThe interface design is the appearance on the screen and the actual manipulation by the user (look and feel) • 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 turner8CS 501 Spring 2002Principles 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 control9CS 501 Spring 2002Disabilities• 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 disabilities10CS 501 Spring 2002Functional 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 zoom11CS 501 Spring 2002Same 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)12CS 501 Spring 2002Data 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)13CS 501 Spring 2002Computer Systems and NetworksThe performance, reliability and predictability of computer systems and networks is crucial to usability• Response timeinstantaneous for mouse tracking and echo of key stroke5 seconds for simple transactions• Example: Pipelined algorithm for the Mercury page turner• Quality of Service for real time information14CS 501 Spring 2002Design Tensions in Networked Systems• Client computers and network connections vary greatly in capacity• Client software may run on various operating systems; it may be current or an earlier version• System designers wish to control clients; users wish to configure their own environments15CS 501 Spring 2002Usability and Cost• Performance may be expensive in hardware or special software development• User interface development may be a major part of a software development project• Costs are multiplied if a user interface has to be used on different computers or migrate to different versions of systemsWeb browsers provide a general purpose user interface that others maintain16CS 501 Spring 2002Usability: Requirements and RefinementIt is very difficult to specify and comprehend an interactive interface in a textual documents.•Requirement documents benefit from sketches, comparison with existing systems, etc.•Design documents should definitely include graphical elements and often benefit from a mock-up or other form of prototype.•Implementation plans should include evaluation of user factors and time to make changes.17CS 501 Spring 2002User Interfaces: Iterative DesignRequirementsDesignImplementation(prototype)Evaluation18CS 501 Spring 2002Methods for Specifying Requirements and Evaluation of Usability• Observing users (user protocols)• Focus groups• Measurements effectiveness in carrying out tasksspeed • Expert review• Client's opinions• Competitive
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