Errors

An ounce of prevention...

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Agenda

ØError typesØSlip typesØError prevention guidelinesØError recovery guidelines

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Error-handling Strategies

1. Avoid and prevent

2. Identify and understand

3. Handle and recover

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Perceptual Errors

ØResult from poor perceptual cuesv Display of objects that are visually similarv Invisible or poorly expressed statesv Failure to capture user’s attentionv Lack of perceivable feedback

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Perceptual Errors

Are perceptual errors likely here?

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Cognitive Errors

ØCaused by taxing memory and thinkingv Tax recall memoryv Poor mnemonic aidsv Inconsistencyv Lack of context or status info

• e.g., where came from in a menuv Mental calculations and translations

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Cognitive Errors

Are cognitive errors likely here?

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Motor Errors

ØTaxing the motor skillsv Awkward movementsv Highly similar motor sequences

• e.g., double click, clickv Pressure for speedv Require a high degree of hand-eye

coordinationv Requiring special types of motor skills (type)

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Motor Errors

Lots of errors are likely here!!

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Slips

ØAutomatic (subconscious) error that occurs without deliberation

ØExamples?

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Types of Slips

Ø1. Capture errorv Continue frequently done activity instead of

intended one• Type “animation” instead of animate• Confirm deletion of file instead of cancel

Ø2. Description errorv Intended action has much in common with

others possible (usually when distracted, close proximity)• ctrl key & caps lock key / Sun & Mac

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Types of Slips

Ø3. Data driven errorv Triggered by arrival of sensory info which

intrudes into normal action• Call to give someone a number, dial that number

instead

Ø4. Associative activationv Internal thoughts and associations trigger

action• Phone rings, yell “come in”

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Types of Slips

Ø5. Loss of activationv Forgetting goal in middle of sequence of

actions• Start going into room, then forget why you’re

going there

Ø6. Mode errorsv Do action in one mode thinking you’re in

another• Delete file, but you’re in wrong directory

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Error Prevention Guidelines

ØEliminate modes or provide visible cues for modes

ØUse good coding techniques (color, style)ØMaximize recognition, minimize recallØDesign non-similar motor sequences or

commandsØMinimize need for typing

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Error Prevention Guidelines

ØTest and monitor for errors and engineer them out

ØAllow reconsideration of action by user (e.g., removing file from trash)

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Error Recovery Guidelines

ØProvide appropriate type of feedbackv Gag - Prevent user from continuing

• Erroneous loginv Warn - Warn user an unusual situation is

occurring• Bell or alert box

v Nothing - Just don’t do anything (Careful, user must determine problem)• Mac: move file to bad place

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Error Recovery Guidelines

ØResponses (continued)v Self-correct - Guess correct action & do it

• Spell-check correctionv Dialog - System opens dialog with user

• Go into debugger on run-time crash

ØQuery - Ask user what should’ve been done, then allow error action as legal one

• Command language naming error

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Error Recovery Guidelines

ØProvide undo functionØProvide cancel function from operations in

progressØRequire confirmation for drastic,

destructive commandsØProvide reasonableness checks on input

datav Did you really mean to order 5000?

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Error Recovery Guidelines

ØReturn cursor to error field, allow fixv Tell them what to fix, how to fix it

ØProvide some intelligencev Guess what they wanted to do

ØProvide quick access to context-sensitive help

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Error Handling Example (Web)

ØForm fill in is the most common error case

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Upcoming

ØHelp & DocumentationØAudioØMobile/Ubicomp