Navigating Complex Information with the ZTree

This paper discusses navigation issues in large-scale databases and proposes hypermap visualizations as effective navigational views. We describe the ZTree, a technique that allows users to explore both hierarchical and relational aspects of the information space. The ZTree uses a fisheye map layout that aids the user in current navigational decisions and provides a history of previous information retrieval paths. 1 Introduction Complex information systems demand different interface approaches from the usual desktop paradigm. People increasingly get lost in electronic space. Navigation is a familiar activity in the real world but a bewildering process in abstract information spaces which lack analogous cues and tools to situate and guide the user along desired routes. The challenge facing us is how to facilitate navigation in such systems without imposing extra cognitive overhead. Complexity in these spaces is a function of size, scope and organisation. One taxonomy defines informati on s truc tures as anarchic (arbitrary organization) vs. moderated (imposed organization) and known (fully defined) vs. unknown (constantly changing) [16]. However, even well-structured and fully-defined spaces can be " unknowable ". In many applications it is the relationships between elements of information that are as interesting as the information itself, and these relationships may be both fixed (imposed by the information model) and dynamic (created by the user as part of the information assimilation task). Further, in many complex spaces it is the user 's path through them (the trace of the information retrieval " dialogue ") that is of interest rather than individual nodes. We use Tweedie's concept of derived [24] rather than fully known structure to express this accumulated set of retrieval paths. A user may derive different structures from the same