The network alignment has been formulated formally. While there are some variations among the tools, the key idea is similar: to combine gene sequence information and protein-protein interaction (PPI) network information to find conserved interaction regions across species. A biological interpretation of network alignment is to find functional homologues across different organisms. The general problem, known as the problem of finding common subgraphs across multiple networks, is NP-hard. Heuristic methods combining sequence, interaction and functional similarities have been developed to...