User Interface Design

Good user interfaces are designed, they don't happen by chance!

• interface design begins with careful analysis of the user, the task and the environment
• user scenarios are created and validated
• prototyping is a common approach to user interface analysis and design.
• early involvement of users makes them more likely to accept the final product
• user interfaces must be field tested and validated prior to general release

• Place User in Control
  • Define interaction in such a way that the user is not forced into performing unnecessary or undesired actions
  • Provide for flexible interaction (users have varying preferences)
  • Allow user interaction to be interruptible and reversible
  • Streamline interaction as skill level increases and allow customization of interaction
  • Hide technical internals from the casual user
    
  • Design for direct interaction with objects that appear on the screen
    
• Reduce User Memory Load
  • Reduce demands on user's short-term memory
    
  • Establish meaningful defaults
    
  • Define intuitive short-cuts
    
  • Visual layout of user interface should be based on a familiar real world metaphor
    
  • Disclose information in a progressive fashion
    
• Make Interface Consistent
  • Allow user to put the current task into a meaningful context
    
  • Maintain consistency across a family of applications
    
  • If past interaction models have created user expectations, do not make changes unless there is a good reason to do so
    
    
• Usability Assessment by Observing Users
  • Is system usable without continual help of instruction?
    
  • Do rules of interaction help a knowledgeable user work efficiently?
    
  • Do interaction rules become more flexible as users become more knowledgeable?
    
  • Has system been tuned to the physical and social user environment?
    
  • Is the user aware of the state of the system?
    
  • Does the user know where he or she is at all times?
    
  • Is the interface structured in a logical and consistent manner?
    
  • Are interaction mechanisms, icons, and procedures consistent across the interface?
    
  • Does the interaction anticipate errors and help users correct them?
    
  • Is the interface tolerant of errors made?
    
  • Is the interaction simple?

• User Interface Design Process (Spiral Model)
  • User, task, and environment analysis and modeling
  • Interface design
    
  • Interface construction
    
  • Interface validation
    
    
  
  
  
  • Interface Analysis Goals
    • Understand people who interact with system through the interface
      
    • Understand tasks end-users must perform to do their work
      
    • Understand the content presented as part of the interface
      
    • Understand the nature of the environment in which tasks will be performed
      
      
  • Analysis of Physical Work Environment
    • Where will the interface be located physically?
      
    • Will the user be sitting, standing, or performing other tasks unrelated to the interface?
      
    • Does the interface hardware accommodate space, light, or noise constraints?
      
    • Are there special human factors considerations driven by environmental factors?
      
      
  • User Analysis Sources
    • User interviews
      • designers meet with end-users individually or in groups
      • do not be swayed by one strong opinion - identify majority
        
    • Sales input
      • sales people help designers categorize users and better understand their needs
        
    • Marketing input
      • marketing analysis can help define market segments
      • can help understand how each segment might use the software
        
    • Support input - support staff can provide good input
      • what works and does not
      • what users like
      • what features generate questions
      • what features are easy to use
        
        
  • Representing Workflow Analysis (swimlane diagram)
    
    
    

• Interface Design
  • Use the information developed during interface analysis to define interface objects and actions (operations)
    
  • Define events (user actions) that will cause the state of the user interface to change and model this behavior
    
  • Depict each interface state as it will appear to the end-user
    
  • Indicate how the user interprets the state of the system from information provided through the interface
    

• Prototype - does not have to be coded during the first iterations
  
  
  
  
• Interface Layout and Content Review Questions
  • Are different types of data assigned to consistent geographical locations on the screen?
    
  • Can user customize screen locations of content?
    
  • Is proper on-screen identification assigned to all content?
    
  • How should large report be partitioned for ease of understanding?
    
  • Will mechanisms be available for moving directly to data summary information for large data collections?
    
  • Will graphical output be scaled to fit bounds of display device used?
    
  • How will color be used to enhance understanding?
    
  • How will error messages and warnings be displayed to the user?
    
    
• Interface Design Issues
  • System response time
    • time between the point at which user initiates some control action and the time when the system responds
      
  • User help facilities
    • integrated, context sensitive help
    • versus add-on help
      
  • Error handling
    • messages should be non-judgmental
    • describe problem precisely
    • suggest valid solutions
      
  • Menu and command labeling
    • based on user vocabulary, simple grammar, and have consistent rules for abbreviation
    • follow widely accepted conventions
      
  • Application accessibility
    • ensuring that interface design contains mechanisms for accommodating user with special needs
    • (vision, hearing, mobility, speech, learning impairments)
      
  • Internationalization
    • interface accommodates needs of different locales and languages
      
      
• User-Interface Development System Capabilities
  • Managing input devices
    
  • Validating user input
    
  • Error handling and displaying error messages
    
  • Providing feedback
    
  • Proving help and prompts
    
  • Handling windows and fields
    
  • Establishing connections between application software and interface
    
  • Insulating application from interface management functions
    
  • Allowing user to customize the interface

• Validation Considerations
  • Does the interface implement every user task correctly, accommodate all task variations, and achieve all general user requirements?
    
  • To what degree is the user interface easy to use and easy to learn?
    
  • Do users' accept that the user interface as a useful tool in their daily work?
    
    
• User Interface Design Evaluation Criteria
  • Length and complexity of written interface specification provide an indication of amount of learning required by system users
    
  • Number of user tasks and the average number of actions per task provide an indication of interaction time and overall system efficiency
    
  • Number of tasks, actions, and system states in the design model provide an indication of the memory load required of system users
    
  • Interface style, help facilities, and error handling protocols provide a general indication of system complexity and the degree of acceptance by the users

Notes and figures from:

• Software Engineering: A Practitioner's Approach, 6th Edition, by Roger S Pressman, R.S. Pressman & Associates, McGraw-Hill, 2005