The size of the graph model to view is a key issue in
graph visualization [8]. Large graphs pose several difficult
problems. If the number of graph elements is large it can
compromise performance or even reach the limits of the
viewing platform. Even if it is possible to layout and display
all the graph elements, the issue of viewability or usability
arises, because it will become impossible to discern between
nodes and edges of graph model. It is well known that
comprehension and detailed analysis of data in graph
structures is easiest when the size of the displayed graph is
small. Since none of the static layouts can overcome the
problems caused by large graphs, hierarchical presentation,
interaction and navigation are essential complements in
information visualization.
In the paper, we consider a practical and general graph
formalism called hierarchical graphs and graph models [11].
It is suited for visual processing and can be used in many
areas where the strong structuring of information is needed
[14]. We present also the Higres and Visual Graph systems
that are aimed at supporting of information visualization on
the base hierarchical graph modes. The Higres system is a
visualization tool and an editor for attributed hierarchical
graphs and a platform for execution and animation of graph
algorithms [9]. The Visual Graph system was developed to
visualize and explore large attributed hierarchical graphs that
present the internal structured information typically found in
compilers [18].