Navigation history

It is normally not possible to give a graphical (or textual) overview of a whole hyperdocument. Some systems offer a fish-eye view, which may be as simple as a list of outgoing links and a picture or list of nodes that have been visited earlier (i.e. a history). Given that history, a hypertext system can easily provide a way to jump to a node in that list. The user can thus backtrack one or more steps through the hyperdocument.

A backtrack facility is certainly necessary for documents that have a hierarchical structure, and thus contain many nodes with no outgoing links. This course is a good example of such a hyperdocument. The structure is not strictly hierarchical, like in a textbook, but for many nodes, there is a subtree below them, with explanations of terms, with more detailed information, or with examples.

Some nodes are a so-called dead-end. After reading such a node the most logical thing to do is to go back to the node you have previously read. Note that the author cannot simply write down which node to go to next, since there may be several links leading to a node, and the author doesn't know beforehand which way you followed.

Most WWW browsers implement only a partial history of your moves. Only the path from the start (index) node to the current node is remembered. (All side tracks you may have taken and backed out of are forgotten.)