Namn: Joakim Sigvald

Titel: Ring Tree and the Hypothesis of Accessibility: Visualisation of
Very Large Information Hierarchies

Abstract:

In this thesis, the area of tree visualisation is investigated, and in
particular its application to web directories. The problem with
today's tree visualisation models is that they provide a poor
overview, while information hierarchies in practice are growing larger
and may contain millions of nodes. Ring Tree is a new tree
visualisation model introduced in this thesis that is designed with
this problem in mind. It can provide an overview of several thousand
nodes that are clearly organised on the screen with little visual
clutter or occlusion. In a series of experiments, Ring Tree has been
compared against two common interfaces for browsing hierarchies 
Explorer and a Yahoo-look-alike interface. Ring Tree, although not
fully developed, performed about as well as the alternative interfaces
and were higher rated by the participants.

The more theoretical part of this thesis investigates the connection
between the task-space and design-space of tree visualisation. The
basic activities of advancement (moving towards the leaves) and
retreatment (moving towards the root) during tree browsing are
identified as especially important for predicting overall
performance. A hypothesis is introduced that, based on this division
of browsing behaviour, describes how differences in interface design
affects performance of different types of tasks. Results from the
experiments with Ring Tree give strong support to this hypothesis. The
results also show that the effect of information scent and information
density on the attentional spotlight suggested by Pirolli et al. [33]
has little, if any, effect on overall performance.