Software Usability

• Quality of user’s experience
• Effectiveness, efficiency, overall satisfaction of user

User Interface (UI)

• Everything that user encounters
• Good UI design: understand the capabilities and limitations of users

Fitt’s Law

• Time required to move to a target
• log(distance / size)

Hick’s Law

• Time to make decision
• log(# of choice)

Cognitive Load Theory

• Perception: Vision has highest information bandwidth
• Memory: Better at recognition than recall
• Miller’s Magic Number: Only about 7 chunks of info held at once by human memory

Mental Model

• Abstract, inner representations regarding things from external world

Interface Gulf(불일치, 간극)

• Gulf within evaluation(of system state) and within execution(of action)

How to Narrow Gulf

Norman’s Design Principle

• Affordance: how things look - how they are used
• Discovery / Visibility: how clear can users know the options and how to access
• Feedback: response to user’s input
• Constraint: limit the range of interaction
• Consistency: similar operations/elements for similar task (i.e., undo & redo)
• Mapping: relationship between control & output

Interface Metaphors

• Help designers deliver mental model
• Conflict with Simplicity, Consistency

Follow Interface Convention

• UI Patterns

UI Design Process

• Design
• Prototype(storyboard, partial implementation, etc.)
• Evaluation
• Requirement Establishment

Usability Evaluation

• Cognitive Walkthrough
  • Designer plays user role
• Heuristic Evaluation
  • Analyze w/ heuristics
• User Test

Usability Heuristics

• System status visibility
• Match between system ↔ real world
• User control & freedom
• Consistency
• Error prevention
• Recognition > Recall (minimize user’s memory)
• Flexibility & Efficiency
• Aesthetic & Minimal (no irrelevant)
• Help recognize, diagnose, recover error
• Help and documentation

Limitations

• Important problems may get missed
• Too focused on minor issue
• Experts are biased

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