ABSTRACT
Every application of network biology typically involves the identification of key nodes, edges, paths, or sub-networks from any given network: these could be essential proteins, key interactions, shortest routes for synthesising a metabolite, or disease-relevant protein modules. A very classic application of network biology is in the identification of functionally important proteins in a given protein–protein interaction network. The classic study in this regard was by Jeong, who proposed the famous centrality–lethality hypothesis. Barabasi, Vidal, and co-workers first developed the concept of disease networks. They represented the disease network as a bipartite graph, where there are two sets of nodes, corresponding to diseases and disease genes. The concept of molecular graphs was introduced by Arthur Cayley as early as 1874, when he created plerograms and kenograms to represent molecular structures. Nodes in these graphs corresponded to molecules, while edges corresponded to covalent bonds.
