Chapter 15: User Interface Design

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Chapter 15 User Interface Design
Design -- A multi-step process in which
representations of data structure, program
structure, interface characteristics, and
procedural detail are synthesized.
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Interface Design

• Three Areas of Concern
• Interfaces between software modules
• Interfaces between software and non-human
  producers and consumers
• For example, sensors and actuators
• Interfaces between the human and computer

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The Golden Rules

• Place the user in control.
• Reduce the users memory load.
• Make the Interface consistent.
• This golden rules actually form the basis for a
  set of user interface design principles that
  guide software design activity.

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1. Place the user in control.

• Define interaction modes that does not force a
  user into unnecessary actions.
• Provide for flexible interaction
• Allow user interaction to be interruptible and
  undoable
• Streamline interaction as skill levels advance
• Hide technical internals from the casual user
• Design for direct interaction with objects that
  appear on screen

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2. Reduce the users memory load

• Reduce demand on short term memory
• Establish meaningful defaults
• Define shortcuts that are intuitive
• Visual layout of interface should be realistic
• Disclose the information in a progressive fashion

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3. Make the Interface consistent

• Allow the user to put the current task into a
  meaningful context
• Maintain consistency across a family of
  applications
• If past interactive models have created user
  expectations, do not make changes unless there is
  a compelling reason to do so.

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INTERNAL EXTERNAL INTERFACE DESIGN

• Intermodular interface design
• DFDs show data flow between modules
• Arrows map into parameters in and out of
  interface
• Determine functions procedures using/producing
  the data
• External interface design
• Typically involves both hardware software
• Often supplied by vendor
• Often complex functionality
• Data validation and error handling

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USER INTERFACE DESIGN MODELS

• Design Model - data, architectural, interface,
  and procedural representations
• User Model - profile of end user, categorization
  as novice, intermittent, or frequent user
  expert
• System Perception - users model end users
  mental image of the system
• System Image - outward appearance and supporting
  information

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USER INTERFACE DESIGN PROCESS

• User, task and environment analysis modeling
• Interface design
• Interface construction
• Interface validation

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The user interface design process
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TASK ANALYSIS MODELING

• Define and classify tasks
• Stepwise elaboration
• Establish goals and intentions for task
• Map goal to sequence of actions as it will be
  executed through the interface
• Specify action sequence
• Indicate state of the system
• Define control mechanism and effects on system
  state
• Indicate how user interprets system state

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DESIGN ISSUES

• System response time - primary user complaint
• Length
• Variability
• User help facilities - integrated vs. add-on
• Scope
• Access methods
• Representation
• How return to normal process
• Structure

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DESIGN ISSUES (cont)

• Error information handling - reduce user
  frustration
• Understandable language
• Constructive advice
• Negative consequences of error
• Audible or visible cue
• Nonjudgmental (dont call user an idiot)
• Command labeling - hot keys vs. point and click
• Scope
• Form
• Ease of use
• Customization or abbreviation

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IMPLEMENTATION TOOLS

• UIDS User Interface Development System
• Managing input devices
• Validating user input
• Handling errors and displaying error messages
• Providing feedback
• Providing help and prompts

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IMPLEMENTATION TOOLS (cont)

• Handling windows and fields
• Establishing connections between application
  software and Interface
• Insulating the application from interface
  management functions
• Allowing the user to customize the interface

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DESIGN EVALUATION

• Length and complexity of written specification
• Number of commands, average number of arguments
  per command, operations per action
• Number of actions, commands, and system states --
  memory load on user
• Interface style, help facilities, and error
  handling protocol

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Interface Design Evaluation Cycle
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End of Chapter