Questions?• Project #2 due soon!• HW#5 out• Midterm: 04/06– Up to (and including) the High Level Theories (03/02)Minimize user memory load• Promote recognition over recall– Recognition is easier than recall• Describe expected input clearly– Don’t allow for incorrect input• Create orthogonal command systems– Using generic commands that can be applied to all interface objectsConsistency• Be consistent in– Command design• Same action, same effect in equivalent situations– Graphic design• Input format• Output format– Flow design• Similar tasks are handled in similar ways• Consistency promotes skills acquisition and/or transferFeedback (Semantic)• Users should always be aware of what is going on– So that they can make informed decision• Be specific– But do not overburden users!– Provide redundant informationFeedback: Toolbar, cursor, ink• Different feedback time scales– Shall I wait for that task to finish or go for coffee?• Different techniques– Short transaction: hour glass cursor– Longer transaction: estimate of time left• An overestimate is always better!Feedback (Time)> 10s10s1s.1s• Different feedback time scales– Shall I wait for that task to finish or go for coffee?• Different techniques– Short transaction: hour glass cursor– Longer transaction: estimate of time left• An overestimate is always better!Feedback (Time)User will switch to another task while waiting> 10sDifficult to stay focused10sDelay but user’s flow of thought is uninterrupted 1sCausality.1sClearly marked exits• Users don’t like to be trapped!• Strategies– Cancel button (or Esc key) for dialog• Make the cancel button responsive!– Universal undoShortcuts (I)• Expert users should be able to perform operations rapidly– Try to limit the training necessary to access advanced features• Strategies– Keyboard and mouse accelerators• menu shortcuts and function keys• command completion, command abbreviations and type-ahead– Toolbars and tool palettes• Trade screen real estate for rapid access– Navigation jumps• History systems– 60% pages are revisitsShortcuts (II)Shortcuts: Keyboard accelerators, toolbars, page size scrolling, launch bar…Preventing errors• Error types– Mistakes• Conscious decision with unforeseen consequences– Slips• Automatic behaviors kicking in– Drive to the store, end-up in the office– Press enter one time too many…• Mode errors– Forget the mode the application is in• Loss of activation– Forget what your goals wereDesigning for slipsOne once of prevention is worth more than a pound of cure!• Examples– Design modeless interfaces– Instead of confirmations provide undo mechanisms– Check for reasonable input• Be prepared to handle several formats• Make entering a incorrect format impossible– Make the current goal clear• Prevent lost of activationsForcing functions• Interlock mechanisms– Switching from P to D in a car• Lockin mechanisms– No eject button for floppy disk on Mac• Lockout mechanisms– Exit stairwaysDealing with errors• People will make errors!– You can ignored them• Generally very confusing– You can correct them automatically• Spelling corrector• But will I trust the system to be right 100%– You can discuss about it• But novice/expert tradeoff– You can try to teach the user what to do• Office assistant• Respect users feelings!Good error messagesFrom Cooper’s “About Face 2.0”• Provide meaningful error messagesGood error messages• Provide meaningful error messages– Explain the problem in term or user conceptual model– Don’t make the user feel stupid– Offer a way to correct the problem– Compare• Error 25: access denied• Cannot open “chapter 5” because “Microsoft Word” is not installed.Do you want to use Notepad instead?Provide help and documentation• Providing help is not an excuse for poor design!– Saving a couple of line of code or writing several pages of documentation?– Users don’t like to read manuals• They prefer to learn while making progress toward their goals• Most users will stay at the intermediate level– Need reminders and a clear learning path– Need a quick way to access critical information• Online documentation and good search toolTypes of help (I)• Tutorial and/or getting started manuals– Presents the system conceptual model• Basis for successful explorations– Provides on-line tours and demos• Demonstrates basic features• Reference manuals– Designed with experts in mind• Reminders– Short reference cards, keyboard templates, tooltips…Types of help (II)•Wizards– Walks user through typical tasks• Users feel they are losing control• What if I do not have the information requested?•Tips– Migration path to learning new features– Can become boring and tediousTypes of help (II)• Context sensitive