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  • 1. CS 502: Computing Methods for Digital Libraries Lecture 21 Usability and user-interfaces
  • 2. Administration
  • 3. Usability Usability of a computer system is a combination of factors: • User interface design • Functionality • Performance • Help systems and documentation • Freedom from errors
  • 4. Levels of usability interface design functional design data and metadata computer systems and networks conceptual model
  • 5. Conceptual model The conceptual model is the user's internal model of what the system provides: • The desk top metaphor -- files and folders • The web model -- click on hyperlinks • Library models search and retrieve search, browse and retrieve
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  • 8. Hierarchical browsing Level 2 Level 1 Level 0
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  • 10. Interface design The interface design is the appearance on the screen and the actual manipulation by the user • Fonts, colors, logos, key board controls, menus, buttons • Mouse control or keyboard control? • Conventions (e.g., "back", "help") Example: Screen space utilization in American Memory page turner.
  • 11. Principles of interface design Interface design is partly an art; there are general principles: • Consistency -- in appearance, controls, and function. • Feedback -- what is the computer system is doing? why does the user see certain results? • Users should be able to interrupt or reverse actions • Error handling should be simple and easy to comprehend • Skilled users offered shortcuts; beginners have simple, well-defined options The user should feel in control
  • 12. Functional design The functional design, determines the functions that are offered to the user • Selection of parts of a digital object • Searching a list or sorting the results • Help information • Manipulation of objects on a screen • Pan or zoom
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  • 15. Same functions, different interface Example: the desk top metaphor • Mouse -- 1 button (Macintosh), 2 button (Windows) or 3 button (Unix) • Close button -- left of window (Macintosh) right of window (Windows)
  • 16. Data and metadata Structural data and metadata stored by the computer system enable the functions and the interface • The desktop metaphor has the concept of associating a file with an application. This requires a file type to be stored with each file: -- extension to filename (Windows and Unix) -- resource fork (Macintosh)
  • 17. Computer systems and networks The performance, reliability and predictability of computer systems and networks is crucial to usability • Response time instantaneous for mouse tracking and echo of key stroke 5 seconds for simple transactions • Example: Pipelined algorithm for the Mercury page turner • Quality of Service for real time information
  • 18. Design tensions in networked systems • Client computers and network connections vary greatly in capacity • Client software may run on various operating systems; it may be current or an earlier version • System designers wish to control clients; users wish to configure their own environments
  • 19. Varieties of user interfaces
    • End user interface. Allows a library user to search , browse , or retrieve known items. Uses structural metadata to present the collections to the user.
    • Librarian and system administrator interface. Provides services for an authenticated user to view , add , delete , or edit digital objects.
    • Batch interface. Provides a method to load large numbers of digital objects automatically.
    • Structure editor. Allows user to review and edit the structure of a collection.
  • 20. Disabilities • What if the user: is visually impaired or color blind? does not speak English? is a poor typist? • There is a tradition of blind programmers • Navigation of web sites need not be only visual
  • 21. Evaluation of usability • Observing users (user protocols) • Focus groups • Measurements effectiveness in carrying out tasks speed • Expert review • Competitive analysis
  • 22. Usability and cost • Performance may be expensive in hardware or special software development • User interface development may be a major part of a software development project • Costs are multiplied if a user interface has to be used on different computers or migrate to different versions of systems Web browsers provide a general purpose user interface that others maintain