16 user interfacedesign

Topics Introduction User-Interface Design Principles User Interaction Information Presentation User Support

User Interface (UI) UI critically important aspect of software engineering System users often judge system by interface rather than its functionality Why? Poorly-designed interface can cause users to make catastrophic errors How? Poor UI design discourages use of software

Graphical UIs (GUIs) Some old systems still use command-line or text-based UIs Most systems today use GUIs Windows: simultaneous views Icons: data, functions Menus: choice of options, memory aids Pointing: trackball, touchpad, mouse, eye Graphics: charts, tables, diagrams Static or dynamic

Examples of GUIs (1) The First Commercial GUI: “ Xerox’s Star workstation was the first commercial implementation of the graphical user interface. The Star was introduced in 1981 and was the inspiration for the Mac and all the other GUIs that followed.” This and following screen shots are from the Computer Desktop Encyclopedia . Used with permission. http://www.computerlanguage.com

Examples of GUIs (2) Macintosh GUI

GUI Advantages Easy to learn and use Save time in training Apply skills to new programs Fast task-switching Use different applications concurrently Information can remain visible in its own window Fast, full-screen interaction possible Immediate access to anywhere on screen Make full use of available “real-estate” Supports multi-screen capabilities

User-Centered Design This chapter / lecture focus: Design philosophy and issues Not on implementation of UIs User-centered design Needs of user are paramount Users involved in design process Design UI through prototypes

UI Design Principles Determinants: learn about system users’ Needs Experience Capabilities Constraints: physical and mental limitations Limited short-term memory 7±2 concepts in mind at one time Mistakes are normal and expected People fall into habits

Design Principles: Overview User familiarity Consistency Minimal surprise Recoverability User guidance User diversity

User Familiarity Interface should be based on user-oriented terms and concepts Avoid using computer concepts E.g., office system: Use “letters, documents, folders” etc. Don’t use “directories, file identifiers” etc.

Consistency Display appropriate level of consistency Commands and menus should have same Format / appearance Command punctuation Layout Abbreviations / keyboard shortcuts Error-messages Same styles / formats from place to place Same location on screen when they appear

Minimal Surprise Extend consistency to commands or actions If one command operates in known way, User should be able to predict operation of comparable commands Put the default choice in the same place or sequence on the screen E.g., Make either YES or NO the default for all commands If keeping a previous file version is default, then don’t make one command delete previous version by default

Recoverability Resilience to user errors Allow user to recover from errors Confirmation of destructive actions ‘ Soft' deletes . . . . Undo / redo facility

User Guidance (1) Help in same place(s) on all screens Context-sensitive Index Topical Smart questions On-line manuals Tutorials . . . .

User Diversity Plan for different types of user Experience Casual/novice vs experienced Ease-of-use vs efficiency & speed Physical disabilities Poor eyesight Configurable font sizes Blindness Automated reading programs US: Americans with Disabilities Act

US ADA & GUI Design Americans with Disabilities Act of 1992 Widespread implications for employment, architectural design and services Applies to private employers with >15 employees, state and local governments, employment agencies & labor unions Web designers have been grappling with requirements Resources http://consumerlawpage.com/brochure/disab.shtml http://academic.evergreen.edu/g/grovesr/acc_class/resources.html

User-System Interaction Key issues Info from user to computer system? Info from computer system to user? UI metaphor helps to make sense of functions “ Desktop” for operating system “ Space invaders game” for typing tutor “ 3D universe” for dataspace (e.g., TRON, Matrix, other sci-fi movies)

Interaction Styles Direct manipulation Menu selection Form fill-in Command language Natural language

Direct Manipulation: Example – PowerPoint Open PowerPoint and study how objects can be Grown Shrunk Flipped Rotated Copied Colored. . . . Through direct manipulation using “tools”

Menu Systems Select from lists of possibilities Point and click with mouse Use cursor keys Type name of selection Touchscreens Usually integrate automated help facilities Help cursor Pop-ups Pop-up text ?

Menu Systems: Benefits Easy to learn – no memorization Reduced typing – faster data entry User errors trapped by interface Context-dependent help

Menu Systems: Problems Best for small # of choices May have to provide sub-menus for complex situations AND and OR relations hard to represent Slower than command language or keyboard shortcuts So provide those as options

Command Interfaces User types commands to give instructions to system e.g. UNIX May be implemented using cheap terminals. Easy to process using compiler techniques Commands of arbitrary complexity can be created by command combination Concise interfaces requiring minimal typing can be created

Command Interfaces: Problems Users have to learn and remember command language. Unsuitable for occasional/casual users Need to be able to type Users make errors in commands Need good error detection and recovery

Natural Language Interfaces User types command in natural language. Vocabulary usually limited Confined to specific application domains; e.g., Timetable enquiries Medical systems Experienced users: too much typing See ASK JEEVES

Information Presentation {numeric, textual} X {static, dynamic} Information may be

Information Display Factors Questions to consider in designing interface Is user interested in precise information or data relationships? How quickly do information values change? Must change be indicated immediately? Must user take some action in response to change? Is there a direct manipulation interface? Is information textual or numeric? Are relative values important?

Data Visualization Concerned with techniques for displaying large amounts of information Visualization can reveal relationships between entities and trends in data Examples of data visualization applications: Weather information collected from number of sources State of telephone network as linked set of nodes Chemical plant visualized by showing pressures and temperatures in linked set of tanks and pipes Model of molecule displayed in 3 dimensions Web pages displayed as hyperbolic tree

Color Displays Color adds extra dimension to interface and can help user understand complex information structures Can be used to highlight exceptional events Common mistakes in use of color in interface design include: Use of color to communicate non-obvious specific meaning E.g., red may mean “hot” to a chemist but “forbidden” to a driver Over-use of color in display – confusing

Guidelines for Effective Use of Color in Displays Don't use too many colors (max 4-5 in window) Don’t use colors as simply as decoration Change of color must imply change of state Use color coding to support tasks Allow users to control color coding Design for monochrome then add color Use color coding consistently Avoid color pairings which clash Use color change to show status change Be aware that color displays usually lower resolution Don’t make large areas of screen BLINK Can cause seizures

User Support User guidance includes On-line help Error messages Manuals Tutorials Integrate help with interface: context-sensitive Integrate help and error messages Easy to get explanation, tips, suggestions Advanced help keeps user profile

Error Messages Bad error messages can lead users to reject entire system Consider background and experience of users in designing messages Messages should be Polite Concise Consistent Constructive Avoid classic errors Never be rude Don’t try to be funny Don’t condescend to your users

Design Factors in Message Wording Context-sensitive Experience – offer verbose / terse modes Skill level – offer beginners / expert modes Style – positive, active (never rude, not funny) Culture – apply localization to avoid offending people in different cultures

System and User-Oriented Error Messages System-oriented message Useful for technical staff Detail internal states of system Good for diagnostics and repair Usually complete gibberish for users User-oriented message Useful for user to fix a problem Reassuring Give instructions on whom to contact if appropriate

A Friendly, Helpful Message System Encourages more positive attitude towards the operating system, the computer and operations: ENTER USER PASSWORD: vs Please enter user password: UNKNOWN SYNTAX vs Pardon? CAN'T INITIATE NEW SESSIONS NOW vs System Alpha not yet available--try again later

A Friendly, Helpful Message System (cont'd) If possible, show what can be done to fix problem Explain WHO can do WHAT to help user in trouble Include telephone numbers OUT OF DISC SPACE (FSERR 46). vs OUT OF DISC SPACE (FSERR 46). Check :FREE for free space Verify :BUILD or :FILE commands for typing error; use 32 extents if possible; check device class; call Ramesh @ (514) 234-5678 X.216 for help

A Friendly, Helpful Message System (cont'd) Gives operators critical information fast Especially important when user gets system information DCU LOGGING IN PROGRESS (THIS IS NORMAL) MAKE LDEV 3 ONLINE RIGHT NOW: PRESS UNLOAD/LOAD STREAMS FACILITY NOT ENABLED Call operations for :STREAMS 10

Help System Design Help? means ‘Help, I want information” Help! means “HELP. I'm in trouble” Both of these requirements have to be taken into account in help system design Different facilities in help system may be required

16 user interfacedesign

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