Table 4 Modules, motifs and graphlets: concepts for decomposing networks into smaller units

are induced subgraphs whose link density is high in comparison to the rest of the graph. This definition is deliberately vague, as what constitutes a module depends on the context and the algorithm used to discover modules.

are small subgraphs, usually of 3 or 4 nodes, whose over- or underrepresentation may indicate that their structures are important or detrimental to the system [21]. Usually, all distinct motifs in a network are counted, yielding a motif signature for the network that may then be compared to signatures obtained by sampling from an appropriate random network null model (see Table 1) to determine over- or underrepresentation. A signature for all motifs on 3 nodes is shown in Figure 1d. Motif signatures can be used to characterize networks.

are similar to motifs but always fully connected. As with motifs, graphlets are used to construct signatures that capture the local characteristics of a network [56].