A Space of Layout Styles for Hierarchical Graph Models of Software Systems

Andreas Noack, Claus Lewerentz
Software Systems Engineering Research Group
Brandenburg University of Technology
Cottbus, Germany

Hierarchical graphs are widely used as models of the structure of
software systems.  A central problem in the visualization of hierarchical
graphs is the computation of layouts, i.e. of positions of
the nodes in two- or three-dimensional space.  We derive requirements
for graph layouts from various software analysis questions,
and classify the required layouts along three dimensions: layouts
with meaningful distances between single nodes vs. layouts with
meaningful distances between groups of nodes, layouts reflecting
adjacency vs. layouts reflecting hierarchy, and layouts that faithfully
reflect the size of subgraphs vs. layouts where certain subgraphs
are magnified.  We present a fairly simple and theoretically
validated energy model for computing such layouts.