  In this paper we present an overview of several visualization techniques to
support the search process in Digital Libraries (DLs). The search process
typically can be separated into three major phases: query formulation and
refinement, browsing through result lists and viewing and interacting with
documents and their properties. We discuss a selection of popular visualization
techniques that have been developed for the different phases to support the
user during the search process. Along prototypes based on the different
techniques we show how the approaches have been implemented. Although various
visualizations have been developed in prototypical systems very few of these
approaches have been adapted into today's DLs. We conclude that this is most
likely due to the fact that most systems are not evaluated intensely in
real-life scenarios with real information seekers and that results of the
interesting visualization techniques are often not comparable. We can say that
many of the assessed systems did not properly address the information need of
cur-rent users.
