HCI in the Software Process

HCI in the software process

• Software engineering and the design process chapter 6 for interactive systems

• Usability engineering

HCI in the software • Iterative design and prototyping

the software lifecycle The waterfall model

Requirements specification • Software engineering is the discipline for Architectural understanding the software design process, or design life cycle Detailed design • Designing for usability occurs at all stages of Coding and the life cycle, not as a single isolated activity unit testing

Integration and testing

Operation and maintenance

Activities in the life cycle Verification and validation

Requirements specification Real-world designer and customer try capture what the system is requirements and constraints expected to provide can be expressed in natural language or The formality gap more precise languages, such as a task analysis would provide Verification designing the product right Architectural design Validation high-level description of how the system will provide the designing the right product services required factor system into major components of the system and how they are interrelated needs to satisfy both functional and nonfunctional requirements The formality gap validation will always rely to some extent on subjective means Detailed design of proof refinement of architectural components and interrelations to identify modules to be implemented separately the refinement Management and contractual issues is governed by the nonfunctional requirements design in commercial and legal contexts

1 The life cycle for interactive Usability engineering systems

cannot assume a linear The ultimate test of usability based on measurement of user Requirements experience specification sequence of activities Usability engineering demands that specific usability measures be Architectural as in the waterfall model made explicit as requirements design Usability specification Detailed – usability attribute/principle design – measuring concept –measuring method Coding and unit testing – now level/ worst case/ planned level/ best case Problems Integration – usability specification requires level of detail that may not be and testing lots of feedback! – possible early in design satisfying a usability specification – does not necessarily satisfy usability Operation and maintenance

part of a usability ISO usability standard 9241 specification for a VCR adopts traditional usability categories: Attribute: Backward recoverability

Measuring concept: Undo an erroneous programming • effectiveness sequence – can you achieve what you want to? Measuring method: Number of explicit user actions to undo current program • efficiency Now level: No current product allows such an undo – can you do it without wasting effort? Worst case: As many actions as it takes to program-in mistake • satisfaction Planned level: A maximum of two explicit user actions – do you enjoy the process? Best case: One explicit cancel action

Iterative design and some metrics from ISO 9241 prototyping

Usability Effectiveness Efficiency Satisfaction • Iterative design overcomes inherent problems of incomplete objective measures measures measures requirements

Suitability Percentage of Time to Rating scale • Prototypes for the task goals achieved complete a task for satisfaction – simulate or animate some features of intended system

Appropriate for Number of power Relative efficiency Rating scale for – different types of prototypes trained users features used compared with satisfaction with •throw-away an expert user power features • incremental • evolutionary Learnability Percentage of Time to learn Rating scale for functions learned criterion ease of learning • Management issues –time Error tolerance Percentage of Time spent on Rating scale for – planning errors corrected correcting errors error handling – non-functional features successfully – contracts

2 Techniques for prototyping Design rationale

Storyboards Design rationale is information that explains why need not be computer-based a computer system is the way it is. can be animated Limited functionality simulations Benefits of design rationale some part of system functionality provided by designers – communication throughout life cycle tools like HyperCard are common for these – reuse of design knowledge across products Wizard of Oz technique – enforces design discipline Warning about iterative design – presents arguments for design trade-offs design inertia – early bad decisions stay bad – organizes potentially large design space diagnosing real usability problems in prototypes…. – capturing contextual information …. and not just the symptoms

Issue-based information Design rationale (cont’d) system (IBIS)

Types of DR: • basis for much of design rationale research • Process-oriented • process-oriented – preserves order of deliberation and decision-making • main elements: • Structure-oriented – emphasizes post hoc structuring of considered issues design alternatives – hierarchical structure with one ‘root’ issue positions – potential resolutions of an issue • Two examples: – Issue-based information system (IBIS) arguments – modify the relationship between positions and issues – Design space analysis • gIBIS is a graphical version

structure of gIBIS Design space analysis

supports Position Argument • structure-oriented responds to Issue • QOC – hierarchical structure: responds to questions (and sub-questions) objects to Position Argument – represent major issues of a design specializes options – provide alternative solutions to the question generalizes Sub-issue criteria questions – the means to assess the options in order to make a choice Sub-issue • DRL – similar to QOC with a larger language Sub-issue and more formal semantics

3 the QOC notation Psychological design rationale

Criterion Option • to support task-artefact cycle in which user tasks are affected by the systems they use • aims to make explicit consequences of design for users Question Option Criterion • designers identify tasks system will support • scenarios are suggested to test task Option Criterion • users are observed on system • psychological claims of system made explicit

Consequent • negative aspects of design can be used to improve next Question … … Question iteration of design

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 Design rationale – recording design knowledge – process vs. structure