Principles of User Interface Design ISMT Multimedia Spring 2000 Dr Vojislav B Misic.

Principles of User Interface Design

ISMT Multimedia Spring 2000Dr Vojislav B Misic

ISMT Multimedia © 2000 Dr Vojislav B Misic Lecture 12/Slide 2

Outline of Lecture 09

(presentation based largely on B. Schneiderman, Designing the User Interface, 3rd ed., Addison-Wesley, 1998

introduction: why, what, how some theories guidelines and principles (rather general) more details and examples


Introduction: Why

Most of today's systems are poorly designed from a human-interaction standpoint

User Interfaces Are Products of Interdisciplinary Work - Who is Involved?

What are the Business Ramifications? Individual User Level International Influences


Life-critical systems

Air traffic control, nuclear reactors, power utilities, police & fire dispatch systems

High costs, reliability and effectiveness are expected

Length training periods are acceptable provide error-free performance

Subject satisfaction is less an issue due to well motivated user

Retention via frequent use and practice


Industrial and commercial uses

Banking, insurance,order entry, inventory management, reservation, billing, and point-of-sales systems

Lower cost may sacrifice reliability Training is expensive, learning must be easy Speed and error rates are relative to cost,

however speed is the supreme concern Subject satisfaction is fairly important to

limit operator burnout


Office, home, and entertainment applications

Word processing, electronic mail, computer conferencing, and video game systems

Choosing functionality is difficult because the population has a wide range of both novice and expert users

Competition cause the need for low cost


Exploratory, creative, and cooperative systems

Database, artist toolkits, statistical packages, and scientific modeling systems

Benchmarks are hard to describe due to the wide array of tasks

With these applications, the computer should "vanish" so that the user can be absorbed in their task domain


Steps For User-interface Engineering

Task analysis to ensure proper functionality Reliability, Availability, Security, and Data

Integrity Standardization, Integration, Consistency,

and Portability Schedules and Budgets (being late means

that you are likely to be ineffective or even noncompetitive)

lifecycle


Task Analysis – Ensure Proper Functionality

Define what tasks and subtasks must be carried out

Pay special attention to those tasks which are only performed occasionally (common tasks are easy to define)

Functionality must complete, or else users will reject or underutilize the product


Reliability, Availability, Security, and Data Integrity

Commands must function as specified Data displayed must reflect the actual state

in the database Appease the user's sense of mistrust System must be error free Ensure the user's privacy by protecting

against unwarranted access, destruction of data, and malicious tampering


Standardization, Integration, Consistency, and Portability

Standardization Integration Consistency:

compatibility across different product versions compatibility with related, non-computer based

systems use common action sequences, terms, units, colors

Portability


System–User Interface Design Goals

Define the target user community associated with the interface (communities evolve and change)

5 human factors central to community evaluation Time to learn Speed of performance Rate of errors by users Retention over time Subjective satisfaction


But, in all cases…

Trade-offs sometimes must be allowed in development, use tools such as macros and shortcuts to ease some burdens

Test all design alternatives using a wide range of mock-ups


Physical abilities and physical workplace

There is no average user, either compromises must be made or multiple versions of a system must be created

Physical measurement of human dimensions are not enough, take into account dynamic measures such as reach, strength or speed

Account for variances of the user population's sense perception


Cognitive and perceptual abilities

cognitive process short-term memory long-term memory and learning problem solving decision making attention and set (scope of concern) search and scanning time perception


Factors affecting perceptual and motor performance

arousal and vigilance fatigue perceptual (mental)

load knowledge of results monotony and boredom sensory deprivation

sleep deprivation anxiety and fear isolation aging drugs and alcohol circadian rhythms


User differences

Personality differences – Myers-Briggs Type Indicator (MBTI) extroversion versus introversion sensing versus intuition perceptive versus judging feeling versus thinking

Cultural and international diversity Users with disabilities Elderly Users


Theories and Principles

Object-Action Interface Model Recognize the diversity Use the Golden Rules of Interface Design Prevent errors Balance of automation and human control


Foley and van Dam four-level approach

Conceptual level: user's mental model Semantic level: meanings conveyed by the

user’s input and computer's output Syntactic level: how the semantic units form

complete sentences and instructions Lexical level: device dependencies and

mechanisms by which a user specifies the syntax


Approach is convenient for designers

Top-down nature is easy to explain Matches the software architecture Allows for useful modularity during design


Action models: Norman's seven stages of action

Forming the goal Forming the intention Specifying the action Executing the action Perceiving the system state Interpreting the system state Evaluating the outcome


Norman's contributions

Context of cycles of action and evaluation Gulf of execution: Mismatch between the

users's intentions and the allowable actions Gulf of evaluation: Mismatch between the

system's representation and the users' expectations


Object/Action Interface Model

Syntactic-semantic model of human behavior used to describe programming database-manipulation facilities direct manipulation


OA Interface Model II

Distinction made between meaningfully-acquired semantic concepts and rote-memorized syntactic details Semantic concepts of user's tasks well-organized

and stable in memory Syntactic details of command languages arbitrary

and required frequent rehearsal

Introduction of GUIs shifts emphasis to simple direct manipulations of visual representations of objects/actions


Object-action design:

understand the task real-world objects actions applied to those objects create metaphoric representations of

interface objects and actions designer makes interface actions visible to

users


Interface hierarchies of objects and actions

Hierarchy is a natural concept Interface includes hierarchies of objects and

actions at many levels Interface Objects (directory, name, length, etc.) Interface Actions (load a text data file, insert into the

data file, save the data file etc.) but note: save file can have many variants

Interface objects and actions based on familiar examples


Learning

Users learn interface objects and actions by seeing a demonstration hearing an explanation of features conducting trial-and-error sessions

Learning, use, and retention of this knowledge is hampered by two problems Details vary across systems in an unpredictable

manner Greatly reduces the effectiveness of paired-associate

learning


How to …

Minimizing these burdens (the goal of most interface designers) aided by Modern direct-manipulation systems Familiar objects and actions representing their task

objects and actions Modern user interface building tools Standard widgets


Four principles of good design

State and the action alternatives should be visible

Should be a good conceptual model with a consistent system image

Interface should include good mappings that reveal the relationships between stages

User should receive continuous feedback


Four critical points where user failures can occur

Users can form an inadequate goal Might not find the correct interface object

because of an incomprehensible label or icon

May not know how to specify or execute a desired action

May receive inappropriate or misleading feedback


Consistent user interface goal

Definition is elusive - multiple levels sometimes in conflict

Inconsistent action verbs Take longer to learn Cause more errors Slow down users Harder for users to remember

Still, it is sometimes advantageous to be inconsistent (but watch out!)


A recent example

Many Florida counties have large numbers of elderly people … whose eyesight is less than ideal

… which is why the US presidential election ballots were designed with larger-than-usual lettering

… which HAD to be split in two pages … and the results is?


Consistent user interface goal

Definition is elusive - multiple levels sometimes in conflict

Inconsistent action verbs Take longer to learn Cause more errors Slow down users Harder for users to remember

Still, it is sometimes advantageous to be inconsistent (but watch out!)


Some examples

Consistency, you said?

Well, let’s see what UST has to say

In most lifts, the control table looks like this … 4th floor at the bottom Open door to the left


However …

There are a few lifts where 4th floor button is NOT at the bottom

Probably because of symmetry – but users have to look

… which they usually do


Wait, there’s more!

There are also some lifts where the Open Door button is NOT on the left …

Which most users DON’T look at – normally, that is


User Interface Metaphor

The way(s) in which users interact with the computer

User interface should resemble a known device or environment


Designer’s model vs. user’s model


Principle 1: Recognize the Diversity

Usage profiles User characteristic Task profiles

Decomposition into multiple middle-level task actions, which are refined into atomic actions

task frequencies of use matrix of users and tasks helpful


Interaction styles

Direct manipulation Menu selection Form fill-in Command language Natural language


Principle 2: Use the Eight Golden Rules of Interface

Design

Strive for consistency (most frequently violated rule)

Enable frequent users to use shortcuts Offer informative feedback Design dialogs to yield closure


Principle 2 cont’d

Offer error prevention and simple error handling

Permit easy reversal of actions Support internal locus of control Reduce short-term memory load


Data Display Guidelines

Goals: Efficient information assimilation by the user Minimal memory load on user Compatibility of data display with data entry Flexibility for user control of data display

Organizing the display Consistency of data display Getting the user's attention


Data Entry Guidelines

Consistency of data-entry transactions Minimal input actions by user Minimal memory load on user Compatibility of data entry with data display Flexibility for user control of data entry


Balance of Automation and Human Control

Ultimate goal: eliminate human actions whenever no judgment is required

real world is open system, while computers constitute closed systems

human judgment necessary for unpredictable events equipment failure improper human performance incomplete or erroneous data


When designing multimedia/hypermedia

Know the users and their tasks Ensure that meaningful structure comes first Apply diverse skills Respect chunking Show interrelationships Ensure simplicity in traversal Design each screen carefully Require low cognitive load


Further reading

Textbook (T. Vaughan): none (actually, there is quite a lot, but … )

Schneiderman’s book: http://www.aw.com/DTUI/

Hall of Fame: http://www.iarchitect.com/mfame.htm

Hall of Shame: http://www.iarchitect.com/mshame.htm

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Principles of User Interface Design ISMT Multimedia Spring 2000 Dr Vojislav B Misic.

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