HCI 3e - Ch 17 (extra):
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HCI 3e - Ch 17 (extra):

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additional slides for Chapter 17: Models of the system...

additional slides for Chapter 17: Models of the system

from
Dix, Finlay, Abowd and Beale (2004).
Human-Computer Interaction, third edition.
Prentice Hall. ISBN 0-13-239864-8.
http://www.hcibook.com/e3/

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    HCI 3e - Ch 17 (extra): HCI 3e - Ch 17 (extra): Presentation Transcript

    • what is state
      • that in the present
      • of that in the past
      • which affects that of the future
      time
    • defining state
      • two problems:
      • too little state
        • elements missing from specification
        • may be deliberate e.g. dialogue level spec.
      • too much state
        • too many states, too complex state
        • may be deliberate redundancy, extensibility
    • too little state
      • forgotten elements
        • e.g. ‘typing’ flag for calculator
      • checking:
        • dialogue state can you work out current dialogue state?
        • action specification do you have enough information?
        • implicit global variables (see also later) suggest state missing
    • too much state
      • unreachable states
        • too few actions (see later)
        • constraints
      • spare variables: constant/functional dependent
      • dependent state
        • e.g. first point of line, number being typed
      • indistinguishable states
        • what is observable?
      states are not orthogonal
    • defining actions
      • framing problems
        • = too little in result state
      • unreachable states – insufficient actions
      • using ‘global’ variables
        • implicit in operation definition
      • beware extreme cases
        • (e.g. empty document, cursor at end of line)