Visualization small PPI network and GO DAG. This plot contains two toy examples of Protein-Protein Interaction network and the Gene Ontology structure. (a) Schematic network of local protein interactions; (b) schematic GO hierarchy, where the thicker link indicates larger weight. Among the neighbors of the central protein in (a), 4 out of 5 are labeled with term A; 2 out of 5 are labeled with term D. One neighbor is not labeled with any term. We want to predict whether or not the central protein has term D.