Chapter XVI: Generating and Adjusting Web Sub-Graph Displays for Web Navigation

Wei Lai, Swinburne University of Technology, Australia
Maolin Huang, University of Technology, Australia
Kang Zhang, University of Texas at Dallas, USA

A graph can be used for web navigation. The whole of cyberspace can be regarded as one huge graph. To explore this huge graph, it is critical to find an effective method for tracking a sequence of the graph's subsets (web sub-graphs) based on the user 's focus.

This chapter introduces our method for generating and adjusting web sub-graph displays in the process of web navigation. Any online web subgraph should fit in the display window. To enhance the display, there should not be any overlap between node images in the web sub-graph. Our system ensures that any online web sub-graph has no overlapping node images by letting the user, or the system itself, define the visible and invisible parts of the web graph.

INTRODUCTION

Most web browsers, such as Netscape and Microsoft Explorer, cannot provide the contextual overview required for global orientation; instead, they can only give a set of URL lists.

A graph is more suitable for World Wide Web (WWW) navigation. Nodes in a graph can be used to represent URLs, and edges between nodes can represent links between URLs. We look at the whole cyberspace of the WWW as one graph ” a huge and dynamic growing graph. However, it is impossible to display this huge graph on the computer screen.

Most current research interests involve "site mapping" methods (see Chen & Koutsofios, 1997; Maarek & Shaul, 1997; Pilgrim & Leung, 1996). That is, they try to find an effective way of constructing a structured geometrical map for one web site (a local map). This can only guide the user through a very limited region of cyberspace, and it does not help users in their overall journey through the cyberspace.

Huang et al. (1998) proposed an online exploratory visualization approach, which provides a major departure from traditional site-mapping methods. It does not pre-define the geometrical structure of a specific web site (a part of cyberspace); instead, it incrementally calculates and maintains a small visualization of a subset of cyberspace online, corresponding to the change of the user's focus. That is, it automatically displays a sequence of web subgraphs with smooth animation following the user's orientation. This feature enables the user to logically explore cyberspace without requiring the whole structure of the cyberspace to be known.

However, the Huang et al. (1998) approach uses the FIFO (first in and first out) rule to animate web sub-graphs, which cannot help the user define a web sub-graph. Also, this approach cannot ensure that its web sub-graph layout has no overlapping node images. This chapter introduces an approach for web graph displays that can overcome these drawbacks.

To aid in web navigation using graphs, we should provide clear web graph displays so that the user can easily understand the relationships shown in a web graph. This requires that interaction facilities should be provided to the user for defining and adjusting a web sub-graph. Automatic web sub-graph displays, based on the user's current focus, should fit in the display window and should have no overlaps.

Two major features of our web graph displays are introduced in this chapter. One is that the user can interact with the web graph to let a node's subgraph be visible or invisible. The other is that overlapping node images/subgraphs are automatically detected and defined as visible or invisible, based on the user's selection.