Location: Hypertext Review / User Interface Issues / Designs for Navigation / BackTracking, History, ... Site Map

2.6 Backtracking, History Lists, Timestamps, and Footprints

Backtracking allows visiting previously visited nodes. Backtracking in a linear fashion and also the ability to arbitrarily jump to previous nodes helps people to bail out of difficult situations. The most preferred method is the path-following principle which allows traversing, in reverse order, those nodes that were previously visited since this approach relies on the user’s memory of his or her own navigation behavior. The structure-oriented feedback approach allows users to directly jump to a node without backtracking. However, experiments have shown that combining these two methods might lead to confusion [Nielsen, 1990a].

Backtracking has been provided in system such as Guide and HyperCard. However, most backtracking mechanisms do not support the feature of going forward to the node from which the backtracking was initiated. Also, backtracking can confuse users if the interface is not consistent. In a document designed with Guide when readers returned from a backtracking operation the display looked different making them wonder whether that was the node they were viewing before taking off on the backtrack [Nielsen, 1990b]. Hence, Nielsen suggests that backtracking mechanisms must fulfill two requirements – “It should always be available, and it should always be activated in the same way.”

A textual history list mechanism was developed for NoteCards which maintains an ordered list of each notecard that was examined in a particular session. Users can select an item from the list and look through a browser. Nodes that have already been visited in a session are marked with a plus sign, one for each time visited. Visual indicators such as the plus sign or checkmarks or asterisks serve as “footprints” on overview diagrams and help users to avoid returning to nodes that have been recently visited. Some implementations of the history list allow users to customize the list for future interaction. A variation of the history list called the history tree shows the users “how” they traversed a set of linked nodes, the digressions, and multiple visits to nodes. Both the history list and history tree can be saved and annotated with text and graphics [Utting & Yankelovich, 1989].

HyperCard has a graphical history list called the recent list which has miniature snap-shots of the last forty-two nodes visited. Clicking on a miniature brings that card to the display. Of course, this method makes the assumption that an individually may not be able to remember the name of the node but may remember the “look” of the node. Some usability studies have shown that it is very difficult for users to distinguish these miniatures from one another [Nielsen, 1990a].

Nodes that are visited can be timestamped (along with the accumulated time spent at each node) and maintained in a chronological order [Nielsen, 1990a]. This feature will help users, at a later date, to recognize whether the node was visited before and if so, the duration allowing users to change their viewing behavior accordingly. The Document Examiner supports a history of commands executed and a history of documents examined. The command history allows people to see previously executed commands and the document history is in the form of bookmarks for each document that was previously opened.