introduction
1. human
2. computer
3. interaction
4. paradigms
5. design basics
6. software process
7. design rules
8. implementation
9. evaluation
10. universal design
11. user support
12. cognitive models
13. socio-organizational
14. comm and collab
15. task models
16. dialogue
17. system models
18. rich interaction
19. groupware
20. ubicomp, VR, vis
21. hypertext and WWW
references

CHAPTER 17
models of the system

outline

links

resources

exercises

We need to know what a system does in order to assess its usability.

• Standard software engineering formalisms can be used to specify an interactive system. These are of various types:
  • model based, such as Z, which describe the system's state and operations
  • algebraic formalisms, which describe the effects of sequences of actions
  • temporal and deontic logics, which describe when things happen and who is responsible.
• Special interaction models are designed specifically to describe usability properties, including:
  • predictability and observability - what you can tell about the system from looking at it
  • reachability and undo - what you can do with it.
• Most formal models and notations focus on events and changes that happen when they occur, but we need richer models to deal with:
  • interstitial behavior - the things that happen between events such as dragging an icon
  • physical objects in ubiquitous computing or virtual reality
  • the tension between precise time and more fuzzy human ideas of time.