exercises

17. models of the system

EXERCISE 17.6

Experiment with the 'back' button on different browsers, help systems, etc. Record systematically the behaviour as you visit pages and use the 'back' button, and try to build a model (informal or formal) of the system. Pay particular attention to what happens if you revisit the same page during the same 'drill down' and the behaviour in systems with multiple windows/frames. (Note that this behaviour does differ dramatically even between different versions of the same web browser.)

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Careful analysis should yield some interesting results. If A, B, C and D are four different pages all with links to one another, a series of 'undos' after visiting the pages in the following order: A, B, C, B, D should give very different results. Most systems keep some sort of stack of states, but in different systems this may be either ABCBD (the full history, common on most web browsers), or ACBD (ignore the earlier visit to B), or ABCD (ignore repeat visits to B). See the links for Chapter 17 on the textbook's web site www.hcibook.com/e3/chaps/ch17/links/ for a paper on history and backtracking, which includes formal models of three different systems.

Other exercises in this chapter

ex.17.1 (ans), ex.17.2 (ans), ex.17.3 (ans), ex.17.4 (ans), ex.17.5 (tut), ex.17.6 (tut), ex.17.7 (tut), ex.17.8 (tut), ex.17.9 (tut), ex.17.10 (tut)

all exercises for this chapter