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CENG 394Introduction to Human-Computer Interaction

CENG 394HCIHCI in the software process

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HCI in the software process

Software engineering and the design process for interactive systems

Usability engineering

Iterative design and prototyping

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the software lifecycle

Software engineering is the discipline for understanding the software design process, or life cycle

Designing for usability occurs at all stages of the life cycle, not as a single isolated activity

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The waterfall model

Requirementsspecification

Requirementsspecification

Architecturaldesign

Architecturaldesign

Detaileddesign

Detaileddesign

Coding andunit testingCoding andunit testing

Integrationand testingIntegrationand testing

Operation andmaintenance

Operation andmaintenance

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Activities in the life cycle

Requirements specificationdesigner and customer try capture what the system is expected to provide can be expressed in natural language or more precise languages, such as a task analysis would provide

Architectural designhigh-level description of how the system will provide the services required factor system into major components of the system and how they are interrelated needs to satisfy both functional and nonfunctional requirements

Detailed designrefinement of architectural components and interrelations to identify modules to be implemented separately the refinement is governed by the nonfunctional requirements

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Verification and validation

Verificationdesigning the product right

 Validationdesigning the right product

 The formality gap

validation will always rely to some extent on subjective means of proof

Management and contractual issuesdesign in commercial and legal contexts

Real-worldrequirementsand constraints The formality gap

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The life cycle for interactive systems

cannot assume a linearsequence of activities

as in the waterfall model

lots of feedback!

Requirementsspecification

Requirementsspecification

Architecturaldesign

Architecturaldesign

Detaileddesign

Detaileddesign

Coding andunit testingCoding andunit testing

Integrationand testingIntegrationand testing

Operation andmaintenance

Operation andmaintenance

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Usability engineering

The ultimate test of usability based on measurement of user experience

Usability engineering demands that specific usability measures be made explicit as requirements

Usability specification usability attribute/principle measuring concept measuring method now level/ worst case/ planned level/ best case

Problems usability specification requires level of detail that may not be possible early in

design satisfying a usability specification does not necessarily satisfy usability

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part of a usability specification for a VCR

Attribute: Backward recoverability

Measuring concept: Undo an erroneous programming sequence

Measuring method: Number of explicit user actionsto undo current program

Now level: No current product allows such an undo Worst case: As many actions as it takes to

program-in mistake Planned level: A maximum of two explicit user actions Best case: One explicit cancel action

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ISO usability standard 9241

adopts traditional usability categories:

effectiveness can you achieve what you want to?

efficiency can you do it without wasting effort?

satisfaction do you enjoy the process?

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some metrics from ISO 9241

Usability Effectiveness Efficiency Satisfactionobjective measures measures measures

Suitability Percentage of Time to Rating scale for the task goals achieved complete a task for satisfaction

Appropriate for Number of power Relative efficiency Rating scale fortrained users features used compared with satisfaction with

an expert user power features

Learnability Percentage of Time to learn Rating scale forfunctions learned criterion ease of learning

Error tolerance Percentage of Time spent on Rating scale for errors corrected correcting errors error handling successfully

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Iterative design and prototyping

Iterative design overcomes inherent problems of incomplete requirements

Prototypes simulate or animate some features of intended system different types of prototypes

throw-away incremental evolutionary

Management issues time planning non-functional features contracts

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Techniques for prototyping

Storyboardsneed not be computer-basedcan be animated

Limited functionality simulationssome part of system functionality provided by designerstools like HyperCard are common for these Wizard of Oz technique

Warning about iterative designdesign inertia – early bad decisions stay baddiagnosing real usability problems in prototypes….

…. and not just the symptoms

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Why prototype? Evaluation and feedback are central to interaction design Stakeholders can see, hold, interact with a prototype

more easily than a document or a drawing Team members can communicate effectively You can test out ideas for yourself It encourages reflection: very important aspect of design Prototypes answer questions, and support designers in

choosing between alternatives

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What to prototype?

Technical issues

Work flow, task design

Screen layouts and information display

Difficult, controversial, critical areas

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Low-fidelity Prototyping Uses a medium which is unlike the final medium, e.g. paper,

cardboard

Is quick, cheap and easily changed

Examples:sketches of screens, task sequences, etc‘Post-it’ notesstoryboards‘Wizard-of-Oz’

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Storyboards

Often used with scenarios, bringing more detail, and a chance to role play

It is a series of sketches showing how a user might progress through a task using the device

Used early in design

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Sketching

Sketching is important to low-fidelity prototyping

Don’t be inhibited about drawing ability. Practice simple symbols

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Card-based prototypes

• Index cards (3 X 5 inches) • Each card represents

one screen or part of screen• Often used in website

development

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‘Wizard-of-Oz’ prototyping• The user thinks they are interacting with a computer, but a developer is responding to output rather than the system.

• Usually done early in design to understand users’ expectations

>Blurb blurb>Do this>Why?

User

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High-fidelity prototyping• Uses materials that you would expect to be in the

final product.

• Prototype looks more like the final system than a

low-fidelity version.

• For a high-fidelity software prototype common

environments include Macromedia Director, Visual

Basic, and Smalltalk.

• Danger that users think they have a full

system…….see compromises

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Compromises in prototyping•All prototypes involve compromises

•For software-based prototyping maybe there is a slow response? sketchy icons? limited functionality?

•Two common types of compromise• ‘horizontal’: provide a wide range of

functions, but with little detail• ‘vertical’: provide a lot of detail for only a

few functions•Compromises in prototypes mustn’t be ignored. Product needs engineering

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Summary

The software engineering life cycle distinct activities and the consequences for interactive system design

Usability engineering making usability measurements explicit as requirements

Iterative design and prototyping limited functionality simulations and animations

Four basic activities in the design process1. Establishing requirements2. Designing alternatives3. Prototyping4. Evaluating

User-centered design rests on three principles1. Early focus on users and tasks2. Empirical measurement using quantifiable & measurable usability criteria3. Iterative design