Today:

AF Chapter 1 – Goal-Directed DesignAF Chapter 2 - Implementation Models and Mental Models

Initiate

The Evolution of the Software Development Process

Design begins to precede the programming process…Formally defining the user and the user’s goals drives the entire development effort

Testing and design became separate steps…Testing in case the code needed fixing; GUI design after coding was done

Code/Test Ship Originally, programmers did it all…Design, code, test, and ship

PROGRAMMERS

Code/TestManagers brought order…

Understanding the market and the competition

PROGRAMMERSMANAGERS

Code Ship

PROGRAMMERS

Initiate

MANAGERS

Test GUI Design

QUALITY ASSURANCE DESIGNERS

Design Ship

DESIGNERS

Initiate

MANAGERS

Code Bug Test

PROGRAMMERS QUALITY ASSURANCE

User TestUSABILITY PRACTITIONERS

Ship

What do people desire?

Of the things people desire, what will

sustain a business?

Of the things people desire that will sustain

a business, what can we build?

Building Successful SoftwareBalancing Desirability, Viability, and Technology

OBJECTIVE:A PRODUCT

THAT IS DESIRABLE, VIABLE, AND BUILDABLECommon Error #1Common Error #1

Emphasize Technology &Emphasize Technology &Ignore DesirabilityIgnore Desirability

(e.g., Silicon Graphics)(e.g., Silicon Graphics)

Common Error #2Common Error #2Emphasize DesirabilityEmphasize Desirability

& Ignore Viability& Ignore Viability(e.g., Napster)(e.g., Napster)

Common Error #3Common Error #3Emphasize Viability &Emphasize Viability &

Ignore DesirabilityIgnore Desirability(e.g., Microsoft)(e.g., Microsoft)

Bridging The Research/Design GapThe Traditional Model

RESEARCHPerformed by market analysts and

ethnographers (immersive cultural observers)

DESIGNPerformed by graphical interface

and industrial designers

The Goal-Directed Design Model

RESEARCHInterview the user and observe the

domain

MODELINGAnalyze the field research, looking

for patterns

REQUIREMENTSDefine and prioritize the needs of the user

and the business

FRAMEWORKUse design patterns

and principles to conceptualize design

REFINEMENTClarify, revisit,

validate, and, finally, document the design

Overview: Goal-Directed Design Process

Research & Modeling•Who will use the product?•What problem will it solve for them?

Requirements & Design•What is the product and what does it contain?•What does it look like and how does it behave?

ScopeDefine the project’s intent and

constraintsAudit

Review existing work and product

InterviewsDiscuss values, issues, and expectations

ObservationsApply ethnographic research techniques

PersonasDefine typical users

GoalsDeduce what users want

RequirementsImagine a system to help users reach goals

ScenariosTell stories about ideal user experiences

ElementsDerive components based on

users

FrameworkOrganize the components

SpecificationsRefine details and describe models

There is frequently a marked contrast between the user’s mental model of how software works and the developer’s implementation

model of how it actually works.

Chapter 2: Implementation Models and Mental Models

User’s Mental ModelsExample: A scientist’s mental model of a technical paper

Title

Authors

Abstract

Body

Body (end)

References

Body (cont.)

The user’s mental model of the process of searching for and purchasing an article from an on-line system

Key Assumptions:• Articles are peer-reviewed

and published in journals• Articles are first published in

print & later on-line• Articles are available in

publisher’s on-line database• Article and meta-data are

stored in the same place• Paying for articles is a

reasonable business expense

Developer’s Implementation ModelsAn implementation model of a technical paper

Key Assumptions:• Articles are peer-reviewed and published in journals• Articles are simultaneously published in print & on-

line• Article data and meta-data are stored on separate

databases (technical constraint)• Paying for articles is a reasonable business expense

Article: Collection of Related Information

Meta-Data:• Authors• Title• Abstract• References

• Publication Date• Journal• Volume/Issue• Etc.

Data:• Article Text• Figures• Tables

The implementation model of the process of

searching for and purchasing an article

from an on-line system

Designer’s Represented ModelsShould the designer represent the software to the user in a manner closer to the developer’s implementation model...?

… or closer to the user’s mental model?

Happy Developer

Unhappy User

Unhappy Developer

Happy User

The designer must develop a third

model that combines the simplicity of the user’s mental model

with the technical veracity of the

developer’s implementation

model.

Design Methods Supporting Mental Models

1. SimplicityMental models simplify reality, so interface design should simplify actual software functionality.• Include only needed functions• Make frequently used

functions immediately apparent

• Avoid cluttering the interface with advanced functions

• Organize the interface to fade into the background, allowing users to focus

Threshold of IndignationAt what point does the performance of a software product fail to

compensate for its complexity of use?

Threshold of IndignationThreshold of Indignation

Willingness/Willingness/Ability to PayAbility to Pay

Consumer TrendsAs time progresses, the attitudes of consumers change…

Threshold of IndignationThreshold of Indignation

Willingness/Willingness/Ability to PayAbility to Pay

Individual ConsumersIndividual Consumers

Can’t pay more, but willing Can’t pay more, but willing to endure greater to endure greater

complexity as they become complexity as they become more accustomed to old more accustomed to old

complexity and as features complexity and as features expandexpand

Industrial/Military ConsumersIndustrial/Military Consumers

Willing to continue high Willing to continue high payments as long as payments as long as

technology improves in technology improves in performance and performance and

becomes easier to usebecomes easier to use

Software Industry TrendsAs time progresses, the technological and business sides

of the software industry evolve…

Threshold of IndignationThreshold of Indignation

Willingness/Willingness/Ability to PayAbility to Pay

Business

Exp

ansion

Business

Exp

ansion

Customer base Customer base tends to lose tends to lose

regard for regard for business if prices business if prices decrease, but will decrease, but will

not accept not accept increases without increases without being convinced being convinced of technological of technological

advancesadvancesHig

h-Tech

Pro

ducts

High-T

ech P

roduct

s

Mass production Mass production and and

technological technological progress progress improve improve

performance performance (lessening (lessening

resistance to resistance to complexity) complexity)

while lowering while lowering costscosts

Design Methods Supporting Mental Models

2. FamiliarityAn interface should build on users’ prior knowledge and experience.• Allow users to start quickly and make immediate progress• Consistency in an interface reduces a user’s learning curve

Design Methods Supporting Mental Models

3. AvailabilityAn interface should provide visual cues, reminders, lists of choices, etc., automatically or on request.• People are better at

recognition than at recall

• Avoid relying on the user for file names, previous settings, etc.

Design Methods Supporting Mental Models

4. FlexibilityAn interface should support alternate interaction techniques.• Allow users to choose the

interaction method most appropriate to their situation

• Allow users to use any object in any sequence at any time

• Accommodate a wide range of user skills, physical abilities, interactions, and usage environments

Design Methods Supporting Mental Models

5. FeedbackAn interface should provide complete, continuous feedback regarding the actions taken.• Feedback supporting the

current mental model reinforces it

• Feedback contradicting the current mental model forces it to be modified

Design Methods Supporting Mental Models6. Safety

Users should feel confident in exploring, knowing that they can try an action, view the results, and then undo the action if the result is unacceptable.• Users feel more comfortable

with interfaces in which their actions do not cause irreversible consequences.

Design Methods Supporting Mental Models

7. Perceived AffordancesUsers often conclude what can and cannot be done with an interface just by examining its appearance.• By using real-world representations of objects within its

interface, a software system can provide users with an intuitive sense of the system’s affordances.

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