Designing the User Interface

Theories, Principles, and Guidelines

Course 4, CMC, 23/09/03

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Designing User Interfaces

“Designing user interfaces is a complex and highly creative process that blends intuition, experience, and careful consideration of numerous technical issues”

Ben Shneiderman (1998, 3rd ed.)

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User Interface

• Locus of interaction

• Cushioning buffer

• Visible aspect of the invisible system

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Human-Machine Loop

Perceptual system detects state

Display tells user machine’s state

Controls allow user to affect machine’s state

Effector system operates controls

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Goals of Interactive Systems

• Simplifying user’s tasks– routine tasks– tedious tasks– error-prone tasks

• Eliminating human actions when no judgment is required

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Causes user’s frustration, fear and failure

• Excessive complexity

• Incomprehensible terminology

• Chaotic layouts

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High-quality interactive systems I

• Beyond vague notion of “user friendliness”

• Thoughtful planning

• Sensitivity to user needs

• Diligent testing

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High-quality interactive systems II

• Positive feelings of success, competence, mastery, clarity

• Interface almost disappears• Interface is comprehensible and

predictable• Interface masks underlying computational

complexity• Users remain “in the flow”

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Goals of system engineering

• Adequate functionality (task analysis)

• Reliability

• Standardization

• Schedule and budgetary planning

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Goals of Interface Design• Design and testing of multiple

alternatives– for specific user communities– for specific tasks

• Measurable human factors– time to learn– speed of performance– rate of errors– retention over time– subjective satisfaction

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Guidance for designers

• High-level theories and models

• Middle-level principles

• Specific and practical guidelines

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High-level theories I

• Four-level approach of Foley & van Dam (1990): conceptual-semantic-syntactic-lexical

• GOMS and the keystroke-level model Card, Moran& Newell (1980,1983); Kieras & Polson (1985); Kieras (1988); Elkerton & Palmiter (1991)

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High-level theories II

• Stages-of-actions models: Norman (1988)’s 7 stages of action– forming goal– forming intention– specifying action– executing action– perceiving system state– interpreting system state– evaluating outcome

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High-level theories III

• Consistency through action grammars: Reisner (1981); Payne & Green (1986)– task[Direction, Unit] -> symbol[Direction] +

letter[Unit]– symbol[Direction=forward] -> “CTRL”– symbol[Direction=backward] -> “ESC”– letter[Unit=word] -> “W”– letter[Unit=character] -> “C”

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High-level theories IV• Widget-level theories: Object-Action

Interface Model of Shneiderman (1980, 1981, 1983)– Hierarchies of task objects and actions– Hierarchies of interface objects and actions– Metaphoric representation conveys interface

objects and actions– Tuning of interface objects and actions to fit the

task– Direct manipulation approach to design– Minimizing burdens of syntax

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Middle-level Principles

• Principle 1: recognize diversity

• Principle 2: use the 8 golden rules of interface design

• Principle 3: prevent errors

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Recognize diversity I• Usage profiles

– novice or first-time users– knowledgeable intermittent users– expert frequent users

• Accommodation of one system to different usage classes– level-structured learning– user control of density of informative

feedback

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Recognize diversity II • Task Profiles

– appropriate sets of atomic objects and actions– relative task frequencies

• Primary Interaction Styles– direct manipulation– menu selection– form fillin– command language– natural language

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8 Golden Rules of Interface Design

• Strive for consistency• Enable frequent users to use shortcuts• Offer informative feedback• Design dialogs to yield closure• Offer simple error handling• Permit easy reversal of actions• Support internal locus of control• Reduce short-term memory load

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Prevent Errors

• Correct matching pairs

• Complete sequences of actions

• Correct commands

• Direct manipulation strategies

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Summary

• Task analysis

• “Know thy user”

• Recording task objects and actions

• Construction of suitable interface objects and actions

• Extensive testing

• Iterative refinement

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Points to discuss

• Faulkner, Raskin, Sutcliffe

• Oulanov & Pajarillo

• Usability Evaluation of OPC

• Contribution of Communication and Information Science to HCI