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Usability

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'As we will see, by focusing first on use and usability rather than on features ... the cost of mistakes and misuse by allowing undoing and redoing while also ... – PowerPoint PPT presentation

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Title: Usability


1
Usability
  • From Larry L. Constantine and Lucy A.D. Lockwood,
    Software for Use A Practical Guide to the Models
    and Methods of Usage-Centered Design,
    Addison-Wesley, Reading, MA, 1999.

2
Some Claims
  • Many systems have been constructed with
    development focused almost entirely on internals,
    on processing logic and data organization to
    fulfill narrow concepts of functional objectives.
  • If it works, some would argue, that is enough.
  • As we will see, by focusing first on use and
    usability rather than on features or
    functionality, on users and usage more than on
    user interfaces, systems can be turned into
    better tools for the job that are smaller,
    simpler, and ultimately less expensive.

3
Homo habilisHandy Man
  • Homo habilis developed a characteristic that is
    uniquely human, the technique of making tools
    reference.
  • Humans are tool users
  • All software systems are tools, so software
    developers are tool builders
  • Avram Miller We are toolmakers, not artists
  • Master craftsmen have special-purpose tools
  • Many of our tools are used to build other tools
  • Grow your own toolkit for toolmakers

4
Quality of Use
  • What makes a thing useful?
  • Utility
  • The system does something worthwhile
  • useful enough to justify its expense
  • Capability
  • Able to do what it is supposed to do
  • Utility and Capability are necessary, but not
    sufficient
  • Users must be able to get the software to do its
    thing
  • Usability

5
Usability
  • Highly usable systems are easy for people to
    learn to use and easy for people to use
    productively
  • Help people work more efficiently and make fewer
    mistakes
  • The best systems give pleasure and satisfaction
  • They make people feel good about using them
  • Five facets of usability
  • Learn-ability
  • Remember-ability
  • Efficiency in use
  • Reliability in use
  • User satisfaction
  • Note the need for engineering trade-offs
  • e.g., easy to learn via step-by-step instructions
    may slow down a well-trained user

6
Economics of Usability
  • Developer costs frequently-cited reasons for
    project cost overruns
  • change requests from users
  • overlooked but necessary requirements
  • users lack of understanding of their
    requirements
  • insufficient user-developer communication
  • ? need emphasis on building an understanding of
    the real requirements of users
  • User costs
  • time spent climbing the learning curve
  • lower productivity than is possible
  • user stress, frustration, morale ? mistakes,
    quitting
  • technical support
  • Over time, more features result in LESS usability

7
Approaching Usability
  • Traditional approaches to improving usability
  • Usability testing
  • Style guides and standards
  • Expert consultation
  • Iterative prototyping
  • Alternative Usage-Centered Design

8
Usability testing
  • Usability labs vs. field testing
  • Note beta testing is a poor way to do usability
    testing
  • Cannot test quality into a product
  • It may be too late or too expensive to fix a
    product that fails testing
  • Get some benefit by usability testing of
    prototypes or storyboards
  • Testing only exercises anticipated use
  • Testing implies an inexperienced user (no one has
    used the new system, yet)
  • Usability tests find isolated, focused defects,
    not defects in the overall architecture or
    organization of the interaction
  • Use usability testing to focus on specific issues
  • e.g., the viability of a novel user interface
    feature or for comparing alternative design
    solutions to the same problem
  • e.g., assuring no lingering defects before
    product shipment

9
Style Guides and Standards
  • Platform-specific style guides (e.g., Windows and
    Mac)
  • Required for conformance stamp of approval even
    though they may be wrong for the application at
    hand
  • In-house style guides
  • Standards promote consistency, and consistency is
    a significant factor in making user interfaces
    easier to learn and remember
  • Well-conceived standards and style guidelines can
    reflect the best practices in user interface
    design
  • Standards and guides can save developers time
  • Re-use, dont re-invent
  • Problems too big, inconsistent, not followed,
    incomplete, poorly designed

10
Iterative Development
  • Problem prototyping is not a substitute for
    analysis and design, not an excuse for sloppy
    thinking
  • Prototyping
  • Test feasibility of an approach
  • Serve as a proof-of-concept for a radically new
    approach
  • Effective tool for communication between
    developers and users
  • Be careful that the user (or developer) do not
    see a sophisticated prototype as next to the real
    thing
  • Software engineering is the only engineering
    discipline that tries to sell prototypes as
    finished goods

11
Design Reviews and Expert Opinion
  • Simple, informal ways to solicit comments and
    suggestions and to promote collaboration
  • Avoid long debates and discussions
  • Software professionals tend to have strong
    opinions
  • Quality of review reflects the (in)experience of
    the reviewers
  • Expert review is often expensive, but
    cost-effective
  • Experts are hard to find and trust
  • Expert review does not transfer skills or
    knowledge
  • The developers are as clueless as they were
    before as to why a given design has usability
    problems

12
Built-In UsabilityUsage-Centered Design
  • Interface with Users
  • Design as dialog
  • Usage-Centered Design
  • Pragmatic design guidelines
  • Model-driven design process
  • Organized development activities
  • Iterative improvement
  • Measures of quality

13
Model-driven design process
  • Core, essential, abstract
  • Role model
  • actors and their relationships to system
  • Task models
  • use cases and their structure
  • Content Models
  • tools and materials to be provided by the user
    interface, and their interconnections
  • Mapping to actual environment
  • Operational models
  • operational profiles
  • Implementation model
  • visual design

14
Five Rules of Usability (1-3)
  • Access Rule The system should be usable,
    without help or instruction, by a user who has
    knowledge and experience in the application
    domain but no prior experience with the system
  • Efficacy Rule The system should not interfere
    with or impede efficient use by a skilled user
    who has substantial experience with the system
  • Progression Rule The system should facilitate
    continuous advancement in knowledge, skill, and
    facility and accommodate progressive change in
    usage as the user gains experience with the system

15
Five Rules of Usability (4-5)
  • Support Rule The system should support the real
    work that users are trying to accomplish by
    making it easier, simpler, faster, or more fun by
    making new things possible
  • Context Rule The system should be suited to the
    real conditions and actual environment of the
    operational context within which it will be
    deployed and used

16
Six Principles of Usability (1-3)
  • Structure Principle Organize the user interface
    purposefully, in meaningful and useful ways that
    put related things together and separate
    unrelated things based on clear, consistent
    models that are apparent and recognizable to
    users
  • Simplicity Principle Make simple, common tasks
    simple to do, communicating clearly and simply in
    the users own language and providing good
    shortcuts that are meaningfully related to longer
    procedures
  • Visibility Principle Keep all needed tools and
    materials for a given task visible without
    distracting the user with extraneous or redundant
    information What You See is What You Need
    (WYSISYN)

17
Six Principles of Usability (4-6)
  • Feedback Principle Through clear, concise, and
    unambiguous communication, keep the user informed
    of actions or interpretations, changes of state
    or condition, and errors or exceptions as these
    are relevant and of interest to the user in
    performing tasks
  • Tolerance Principle Be flexible and tolerant,
    reducing the cost of mistakes and misuse by
    allowing undoing and redoing while also
    preventing errors wherever possible by tolerating
    varied inputs and sequences and by interpreting
    all reasonable actions reasonably
  • Reuse Principle Reduce the need for users to
    rethink, remember, and rediscover by reusing
    internal and external components and behaviors,
    maintaining consistency with purpose rather than
    merely arbitrary consistency
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