Hypermedia – Paths and Trails
2.4 Paths and Trails
In most current hypertext systems, readers have a problem trying to understand the material presented because they view it in the wrong order or they simply cannot comprehend easily. The concept of a path can help solve this problem by allowing authors to determine an appropriate order of presentation for a given audience. It will reduce both disorientation and cognitive overhead since users will follow a pre-defined path which will also narrow down their choices. The concept of paths or trails was first enunciated by Bush in his classic paper, “As We May Think”. He called a trail a sequence of links through a memex.
“The process of tying two items together is the important thing [...] Before him are the two items to be joined, projected onto adjacent viewing positions [...] he user taps a single key, and the items are permanently joined [...] Thereafter, at any time, when one of these items is in view, the other can be instantly recalled merely by tapping a button [...] oreover, when numerous items have thus been joined together to form a trail, they can be reviewed in turn, rapidly or slowly [...] It is exactly as though the physical items had been gathered together from widely separated sources and bound together to form a new book. It is more than this, for any item can be joined into numerous trails [...] rails do not fade [...] everal years later, [...] tapping a few keys projects the head of the trail. A lever runs through it at will, stopping at intersecting items, going off on side excursions.” [Bush, 1945].
The idea of trails was implemented as paths by Trigg in his TEXTNET system. In Intermedia, a path is a list of documents users visited earlier in a browsing session. The display of a path consists of the name of the document, an icon indicating the type of event (opening or activating documents), and a timestamp indicating when the event occurred. A user’s path is saved when closing the web and restored when opening the web, the next time. Thus, a path can be used to collect all interesting documents to form a linear document that can be preserved in printed form [Utting & Yankelovich, 1989].
The Scripted Documents System, developed at XEROX, uses paths which are procedural and programmable. The items in the path (nodes) can be “active” entries or scripts which can do computations, execute programs etc. The entries provide the content while the path provides sequencing. Paths can be created and edited using path editors. Readers can get local and global views of relevant paths. Playback mechanisms are supported which allow users to play back a path either single-stepped or automatic. Different kinds of scripts provide different paths and can be used to create presentations for different classes of audiences [Zellweger, 1989].