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User Interface Design
Lecture 4Lecture 4
Requirements Gathering: Knowledge f U I f D iof User Interface Design
C. Patanothai 2110646:04‐Knowledge of User Interface Design 2
Knowledge Types for UI DesignKnowledge Types for UI Design
• Information‐gathering activities and analyses that form part of the user interface designthat form part of the user interface design and development process
• User interface design knowledge, from theory (cognitive psychology), and experience (studying designs that areexperience (studying designs that are currently working well.
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Minimizing workMinimizing work
C iti k• Cognitive work– comprehension of product behaviors
• Memory work• Memory work– recall of product behaviors, commands, names and locations of objects and controls and other relationships b bbetween objects
• Visual workwhere the eye should start on a screen finding object– where the eye should start on a screen, finding object, decoding layouts
• Physical worky– keystrokes, mouse movement, gesture (click, drag, double‐click), switching between input modes, # of clicks required
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Design KnowledgeDesign Knowledge
D i P i i l• Design Principles– derived from experienceabstract high level guides– abstract, high‐level guides
– general, difficult to apply– First Principles of Interactive Design– First Principles of Interactive Design
• Design Rules• Design Rules– low‐level– high specific instruction– high specific instruction– 8 Golden Rules
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4 Psychological Principles4 Psychological Principles
U h t th t t• Users see what they expect to see
• Users have difficulty focusing on more than• Users have difficulty focusing on more than one activity at a time
• It is easier to perceive a structured layout
It i i t i thi th t t• It is easier to recognize something that to recall it
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4 Psychological Principles4 Psychological Principles
Users See What They Expect to See
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ExerciseExercise
• Look at figure and read it.
• Anything strange?Anything strange?
• Principle of consistency– throughout the UIthroughout the UI
• Principle of exploiting prior knowledge– users perceive the screen using their prior knowledge
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4 Psychological Principles4 Psychological Principles
Users Have Difficulty Focusing on More Than One Activity at a Time
– The Cocktail Party Effect
– Principle of Perceptual OrganizationG lik thi t th• Group like things together
– Principle of Importance• Prominent display for important items
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4 Psychological Principles4 Psychological Principles
It Is Easier to Perceive a Structured Layout
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4 Psychological Principles4 Psychological Principles
Gestalt principlesa. Proximityy
b. Similarity
c Closurec. Closure
d. Continuity
e. Symmetry
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Figure‐Ground SegregationFigure Ground Segregation
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Exercise (5 minutes)Exercise (5 minutes)
How well does this web sites support the principles of proximity, similarity, p y, y,closure, and continuity?
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4 Psychological Principles4 Psychological Principles
It Is Easier to Recognize Something Than to Recall ItRecall It
• Principle of recognitionp g• Knowledge in the head & Knowledge in the world• exceptionsexcept ons
• expert prefer key combinations• routine operator don’t like to read the same routine operator don t like to read the same
info. repeatedly
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Three Principles from Experience: Visibility, Affordance, and Feedback
The Principle of Visibility: It Should Be Obvious What a Control Is Used ForWhat a Control Is Used For
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Three Principles from Experience: Visibility, Affordance, and Feedback
The Principle of Affordance: It Should Be Obvious How a Control Is UsedObvious How a Control Is Used
ff d t l t ti f‐ affordance: strong clues to operations of things
‐ no picture, label, or instruction is required
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Affordance: actual vs perceivedAffordance: actual vs. perceived
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Three Principles from Experience: Visibility, Affordance, and Feedback
• The Principle of Feedback: It Should Be Obvious When a Control Has Been UsedObvious When a Control Has Been Used
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Principles to support usabilityPrinciples to support usability
L biliLearnabilitythe ease with which new users can begin effective interaction and achieve maximal performanceand achieve maximal performance
Flexibilityythe multiplicity of ways the user and system exchange information
Robustnessthe level of support provided the user in determiningthe level of support provided the user in determining successful achievement and assessment of goal‐directed behaviour
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Principles of learnabilityPrinciples of learnability
di biliPredictability– determining effect of future actions based on past interaction history
– operation visibility
SynthesizabilitySynthesizability– assessing the effect of past actions on the current statestate
– immediate vs. eventual honesty
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Principles of learnabilityPrinciples of learnability
F ili itFamiliarity– how prior knowledge applies to new system
b l– guessability; – affordance – how any visual object can be manipulatedmanipulated
G li biliGeneralizability– extending specific interaction knowledge to new
it tisituations– within a single app. or across apps.
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Principles of learnabilityPrinciples of learnability
C iConsistency– likeness in input/output behaviour arising from similar situations or task objectivessituations or task objectives
– familiarity – consistency with respect to past real‐world experiencep
– generalizability – consistency with respect to experience with the same system or set of applications on the same l fplatform
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Principles of flexibilityPrinciples of flexibility
Di l i iti tiDialogue initiative– freedom from system imposed constraints on input dialogue– system vs. user pre‐emptivenessy p p– maximize the user pre‐emptive, minimize the system pre‐emptive
MultithreadingMultithreading– ability of system to support user interaction for more than one task at a time
t i t l i lti d lit ( lti h l)– concurrent vs. interleaving; multimodality (multi‐channel)
Task migratability– passing responsibility for task execution between user and system– e.g. spell‐check
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Principles of flexibilityPrinciples of flexibility
S b tit ti itSubstitutivity– allowing equivalent values of input and output to be substituted for each othersubstituted for each other
– representation multiplicity; equal opportunity
Customizability– modifiability of the user interface by user (adaptability) or
t ( d ti it )system (adaptivity)– adaptability – user's ability to adjust the form of input and outputp
• the overall structure of the interaction is unchanged– adaptivity – automatic customization
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Principles of robustnessPrinciples of robustness
Observability– ability of user to evaluate the internal state of the system from its perceivable representation
– browsability;
– defaults;
– reachability;
– persistence;
– operation visibility
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Principles of robustnessPrinciples of robustness
ObservabilityObservability– browsability – allows the user to explore the current internal state of the system via the limited view provided at the i t finterface.
– defaults – system provided values• static or dynamic
– reachability – the possibility of navigation through the observable system states
• affects the recoverability of the system– persistence – the duration of the effect of a communication act and the ability of the user to make use of that effect
• vocal comm. does not persist• visual comm. remains long after the act of presentation• e.g. email notification with beef and envelop flashing
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Principles of robustnessPrinciples of robustness
R biliRecoverability– ability of user to take corrective action once an error has been recognizedrecognized
– linked to reachability since we do not want to block the user from getting to a desired state from some other undesired state
• forward recovery – the acceptance of the current state and negotiation from that state towards the desired state
• backward recovery – undo the effects of previous interaction in d i b f diorder to return to a prior state before proceeding
– commensurate effort – if it is difficult to undo a given effect on the state, then it should have been difficult to do in the first place p(easily undone actions should be easily doable.)
• if it is difficult to recover deleted files, then it should be difficult to remove them.
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Principles of robustnessPrinciples of robustness
R iResponsiveness– how the user perceives the rate of communication with the systemthe system
– stability – the invariance of the duration for identical or similar computational resources
• e.g. pull‐down menus are expected to pop up instantaneously as soon as a mouse button is pressed
Task conformancedegree to which system services support all of the– degree to which system services support all of the user's tasks
– task completeness; task adequacyp ; q y
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Other PrinciplesOther Principles
• Constraints
• Natural mappingNatural mapping
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ConstraintsConstraints
d• Boundary
• Some can be selected, some cannotSome can be selected, some cannot
• physical vs. logical– cannot move cursor outside the screencannot move cursor outside the screen
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Natural MappingNatural Mapping
• Mapping should match functionality
• direct is the bestdirect is the best• natural mapping does not have to be direct
– light switch
– oven control– turn signal
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Poor Physical Natural MappingPoor Physical Natural Mapping
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Good Physical Natural MappingGood Physical Natural Mapping
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Logical MappingLogical Mapping
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