Usability Engineering Part 1

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Usability EngineeringPart 1

• CIS 577
• Bruce R. Maxim
• UM-Dearborn

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Lecture Slides Based onUsability
EngineeringbyLaventhal and Barnes
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What is a User Interface?

• The user interface is the boundary between the
  user and the functioning part of the system.
• The interface may disguise the inner workings of
  the system by relying on metaphors to express the
  users tasks that can be accomplished using the
  system.

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Everyday Objects and the User Interface

• Everyday objects have user interfaces
• Users rarely consider an objects functionality
  separately from its user interface.
• For most users, the user interface is the
  object.

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Learning from Everyday Objects

• Poorly designed user interfaces can impair a
  users ability to use an object.
• Potentially true even if the objetcs
  functionality is very good.
• When an interface is poor, it often reflects an
  inappropriate design process.

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How Do Users Know What to Do with an Interface?

• Objects provide subtle perceptual cues
• What part of the object to operate (i.e., what is
  the interface)/
• What we are supposed to do with the interface.
• How our interaction is constrained by the
  interface and the interfaces.
• What is supposed to happen when we operate the
  interface.

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Perceptibility of Salient Cues from the Interface

• For us to perceive subtle clues about an
  interface, the important parts must be obvious.
• The interface must provide the appropriate
  information for achieving relevant tasks.
• The interface needs to provide information to
  help support the users decision about what needs
  to be done next to achieve a goal.

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User Models of Devices

• We process the information from a device through
  whatever existing internal mental model we have
  about this kind of device.
• We call this a mental model of the device.
• Mental models help us to make predictions about a
  device.

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User Device Models

• The following information is incorporated into
  our mental models of device operation.
• What do you perceive you can do with the user
  interface?
• What are the limitations of the user interface?
• What is supposed to happen when we operate the
  interface?

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In-Class Exercise

• Consider an everyday object in the class room
  (e.g. the display selection box)
• Answer the following questions.
• What is the user interface?
• How do you operate the device?
• How is the operation constrained?
• How is the user input to the interface related to
  the expected function of the object?

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Accuracy of Our Mental Model

• How do we know that our mental model fits the
  device?
• Feedback is a mechanism by which users can adjust
  their mental models.
• What happens when the feedback contradicts out
  mental model?
• Frustration?

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Feedback

• Information perceived from the user interface in
  concert with the users knowledge is used to form
  a mental model of the device and its operation.
• Feedback from the user interface is a way that
  users check and evolve their mental model of a
  device.
• We cannot evaluate the user interface design
  independently of either the users background or
  task context.

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User Friendly? Not!

• User friendly" is an anthropomorphic term.
• Do people want to be friends with your computer
  or its interface?
• User-friendly suggests a one-dimensional
  attribute.
• The system is either user friendly or not!
• Clearly there is a range of usabilty values as
  user interfaces can be more or less usable.

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User Interface Success Factors

• Type of user
• Type of task
• Hardware constraints
• Social and cultural limitations
• Environmental constraints

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Hardware Environments

• Hardware has become much more powerful.
• This has permitted the development of more
  sophisticated user interfaces, such as graphical
  user interfaces.
• Hardware that the user interacts with directly
  (peripherals) has become more diversified.
• This has also contributed to the development of
  different user interfaces.
• Hardware has become more accessible to a wider
  range of users.

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Changes in User Characteristics

• The proportion of professional computer
  scientists to routine users has changed
  dramatically.
• In the western world most people need to interact
  with some type of computing equipment in their
  daily lives.
• Novice users have sophisticated expectations
  about the computer systems that they use.

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Changes in Software Applications

• The software applications that the user interacts
  with directly have become more and more
  diversified.
• Who would have imagined the wide spread use of
  the Internet, cell phones, Ipods, or video games
  by the masses without any programming knowledge.

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Perspective

• Building usable interfaces is difficult.
• Many myths about usability persist.
• Good user interfaces are just appealing graphics.
• Usability is an outcome of common sense.
• Guidelines, applied to user interface problems,
  will lead to usability.
• Usability problems can be solved with
  help/training/documentation.

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What are the Big Issues?

• How do we improve user interfaces and the user
  interface development process?
• What is the future of HCI?
• How can software engineers ensure good usability
  in the systems that they build?

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Defining Usability?

• A dictionary definition is still not detailed
  enough to evaluate whether a system is usable or
  not.
• How could we extend a definition into something
  that could actually be used to evaluate
  usability?
• A model of usability
• describes characteristics of a usable interface
• indicates how those characteristics fit together
• what the characteristics mean.

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Usability

• Usability is the result of the interaction of the
  characteristics of the user interface and the
  situation.
• Usability engineers cannot usually control or
  change the situation.
• The best chance to create a highly usable
  interface is to make design decisions that take
  the situation variables into account.

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Shackels Model of Usability - 1

• Effectiveness
• User performance better than some required level
• By some proportion of the target users
• Within some required range of user environments
• Learnability
• Time required between system installation and
  start of user training
• Based on a specified amount of training and user
  support
• Amount of the relearning time required for
  intermittent users between sessions

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Shackels Model of Usability - 2

• Flexibility
• Allows adaptation to a specified level of
  variation in tasks or environments (beyond the
  original specification)
• Attitude
• Within acceptable measures of human cost
  (tiredness, discomfort, frustration, effort)

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Nielsens Model of Usability
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Easons Model of Usability
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Easons Model of Usability

• Usability is an outcome (dependent variable) that
  results from a combination of system (user
  interface) characteristics and contextual
  variables of user and task.
• Under each of these dimensions (system, user,
  task), Eason gives some ideas of what issues
  affect usability.
• Eason's framework is based on a field study that
  he performed and the variables that he
  highlighted were the one's that he found to be
  important in his study.

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Eason ModelTask Characteristics

• Task is what the user can accomplish with the
  system or device.
• Task characteristics
• Frequency
• Number of times a task is performed by a user.
• Openness
• Extent to which a task is modifiable.
• Task characteristics are independent of the
  platform on which the task is performed.

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Eason ModelUser Characteristics

• Eason recognized that characteristics that the
  user brought to the task and the user interface
  would influence their experience.
• User characteristics
• Knowledge
• The knowledge user applies to the task may be
  appropriate or inappropriate.
• Motivation
• How determined the user is to complete the task.
• Discretion
• User's ability to choose not to use some part of
  a system.

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Eason ModelSystem Characteristics

• In this model the system is the user interface.
• System characteristics
• Ease of learning
• Effort required to understand and operate an
  unfamiliar system.
• Ease of use
• Effort required to operate a system once it has
  been understood and mastered by the user.
• Task match
• Extent to which information and functions a
  system provides matches the needs (goals) of the
  user.

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Applying Causal Models

• Easons model says that usage context, in
  combination with user interface characteristics,
  drive and determine usability.
• Easons model has two parts
• Input is user/system/task characteristics which
  are the main independent variables.
• Outcome is users reaction which is the dependent
  variable.

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What to Do With Usability Models?

• Demonstrate or evaluate existing systems.
• Develop systems with a goal of usability
• Usability models suggest that a usable interface
  will be one that emphasizes
• Ease of learning
• Ease of use
• Good task match
• High levels of user satisfaction

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Building a User Interface

• Building a User Interface is part of the larger
  problem of building a software system.
• Adding a significant user interface to a software
  project requires.
• Support for interactivity.
• Support for media.
• Support for user-tailoring.

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Activities in Software Engineering

• Understanding and documenting the context of the
  project.
• Understanding and documenting the problem to be
  solved
• Designing and documenting a solution in the
  context.
• Implementing the solution.
• Testing and evaluating the solution.

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The Waterfall Model of Software Development
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Benefits of Exactly Following the Waterfall Model

• Following any methodology imposes discipline on
  the software development process.
• Following a phased model improves cost and
  resource forecasting.

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Problems of Following the Waterfall Model

• Has difficulty accommodating uncertainty existing
  at beginning of many projects.
• Does not inherently support iteration.
• Requires customer to completely elaborate
  requirements at the beginning of the project.
• Customer will not see any defects until late in
  the development cycle.

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Spiral Model
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Spiral Model

• Supports incremental ddevlopment
• Early customer involvement
• Uses metrics-based risk assessment with each spin
  to make the go/no go decision
• Requires creation and evaluation of interface
  prototypes

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Star Life Cycle
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Star Life Cycle Is

• Not sequential
• Activities can proceed in any order
• Evaluation-centred
• Each activity is evaluated
• Interconnected
• Thorough the evaluation in the middle

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Usability and Software Engineering

• In the abstract, the steps for both tasks are the
  same.
• We can set up parallel flows of activities for
  both usability and software engineering.
• The model supports iteration.

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Activities of Usability Engineering

• Understanding and documenting the context of the
  project.
• Understanding and documenting the problem to be
  solved.
• Designing and documenting a solution in the
  context.
• Implementing the solution.
• Testing and evaluating the solution.

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Usability and Software Engineering Activities
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Integrating UE Processes