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familiar ones. In Memex, the idea is to make such connections accessible to other
people. Connections made in this way are called trails. Bush referred to people who
are making such trials as trailblazers. Trailblazers are builders of an ever-growing
information space. Memex itself has never materialized, but it has a gigantic nearest
kin - the World-Wide Web.
We know that the Web relies on hypertext reference links to pull millions of
documents together. In fact, studies of small-world networks have found the Web
has many features of a small-world network. We will return to small-world networks
in later chapters, but here an interesting thing to know is that the Web has a diameter
of about 16, which means that given an arbitrary pair of documents on the Web, we
can reach one from the other by following a chain of, on the average, 16 hyperlinks.
A central issue for the Web is how to make sure that users can find their way in
this gigantic structure. The predecessor of the Web is a group of hyper-referencing-
enabled information systems - hypertext systems. Research in hypertext started in
the late 1980s was marked by a number of classic hypertext systems such as Apple's
HyperCard and the NoteCards from Xerox PARC. Navigation has been a central
research issue for hypertext over the last two decades. For example, Canter and his
colleagues distinguished five types of search in hyperspace (Canter et al.
1985
):
•
Scanning: covering a large area without depth
•
Browsing: following a path until a goal is achieved.
•
Searching: striving to find an explicit goal.
•
Exploring: finding out the extent of the information given.
•
Wandering: purposeless and unstructured globetrotting.
An overview map is a commonly used solution to the notorious lost-in-
hyperspace problem first identified by Jeff Conklin (
1987
). A wide variety of
techniques have been developed over the last two decades for generating overview
maps automatically. The sheer size of the Web poses a tremendous challenge. Many
algorithms developed prior to the Web need to be scaled up before they can handle
the Web. New strategies have been developed to avoid brute-force approaches.
3.1.2
The Origin of Cognitive Maps
The origin of cognitive maps can be traced back to Edward Tolman's famous study
published in 1948 on the behavior of rats in a maze
1
(Tolman
1948
). He studied the
behavior of those rats that managed to find the food placed in a maze and realized
that his rats had obviously managed to remember the layout of the maze. Prior to
Tolman's study, it was thought that rats in a maze were only learning at particular
turning points to make left or right turns. Tolman called this internalized layout a
cognitive map. He further proposed that rats and other organisms develop cognitive
maps of their environments.
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