Analysis of edge-betweenness distribution in the Drosophila PPI network. (a) A theoretical example of a network between 10 vertices linked by 13 edges (both solid and dashed lines) for the 'shortest path' and the 'edge-betweenness' (EB) definitions. The shortest path between two nodes represents the path for which the number of edges is minimized: the shortest path between nodes b and j is represented by the path in dashed lines. The betweenness of an edge represents the number of shortest paths running through it. For instance, the EB value of the edge i-j corresponds to the number of nodes in the rest of the graph; the EB value of the edge a-b is 1, because only the shortest path between the nodes a and b runs through this edge; the EB value of the edge e-g is the higher of the graph since all shortest paths between nodes located on the left part on one hand, and on the right part on the other hand, must run along it. (b) Piecharts showing the repartition of the subsets of edges internal (left) and external (right) to the signalling network among the 4 interquatile intervals of the EB values distribution. For each subset of edges, the interquartile intervals (labelled from 1 to 4) are indicated by the same colors (chart in the middle).