From homogeneous networks to heterogeneous networks of networks via colored graphlets

Research of homogeneous (i.e., single node and edge type) biological networks (BNs) has received significant attention. Graphlets have been proven in homogeneous BN research. Given their popularity, graphlets were extended to their directed or dynamic counterparts, owing to increase in availability of directed or temporal BNs. Given the increasing amounts of available BN data of different types, we generalize current homogeneous graphlets to their heterogeneous counterparts, which encompass different node or edge types and thus allow for analyzing a heterogeneous "network of networks". Heterogeneous graphlets will have at least as high impact as homogeneous graphlets have had. We illustrate the usefulness of heterogeneous graphlets in the context of network alignment (NA). While existing NA methods are homogeneous (they can only account for a single node type and a single edge type), we generalize a state-of-the-art homogeneous graphlet-based NA method into its heterogeneous counterpart. Because graphlets are applicable to many other network science problems, we provide an implementation of our heterogeneous graphlet counting approach (available upon request).