Tree-Like Structures in Graphs: A Metric Point of View

Recent empirical and theoretical work has suggested that many real-life complex networks and graphs arising in Internet applications, in biological and social sciences, in chemistry and physics have tree-like structures from a metric point of view. A number of graph parameters trying to capture this phenomenon and to measure these tree-like structures were proposed; most notable ones being the tree-stretch, tree-distortion, tree-length, tree-breadth, Gromov’s hyperbolicity of a graph, and cluster-diameter and cluster-radius in a layering partition of a graph. If such a parameter is bounded by a constant on graphs then many optimization problems can be efficiently solved or approximated for such graphs. We discuss these parameters and recently established relationships between them for unweighted and undirected graphs; it turns out that all these parameters are at most constant or logarithmic factors apart from each other. We give inequalities describing their relationships and discuss consequences for some optimization problems.