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Uncovering the overlapping community structure of complex networks in nature and society


Many complex systems in nature and society can be described in terms of networks capturing the intricate web of connections among the units they are made of1,2,3,4. A key question is how to interpret the global organization of such networks as the coexistence of their structural subunits (communities) associated with more highly interconnected parts. Identifying these a priori unknown building blocks (such as functionally related proteins5,6, industrial sectors7 and groups of people8,9) is crucial to the understanding of the structural and functional properties of networks. The existing deterministic methods used for large networks find separated communities, whereas most of the actual networks are made of highly overlapping cohesive groups of nodes. Here we introduce an approach to analysing the main statistical features of the interwoven sets of overlapping communities that makes a step towards uncovering the modular structure of complex systems. After defining a set of new characteristic quantities for the statistics of communities, we apply an efficient technique for exploring overlapping communities on a large scale. We find that overlaps are significant, and the distributions we introduce reveal universal features of networks. Our studies of collaboration, word-association and protein interaction graphs show that the web of communities has non-trivial correlations and specific scaling properties.

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Figure 1: Illustration of the concept of overlapping communities.
Figure 2: The community structure around a particular node in three different networks.
Figure 3: Network of the 82 communities in the DIP core list of the protein–protein interactions of S. cerevisiae for k = 4.
Figure 4: Statistics of the k -clique communities for three large networks.

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We thank A.-L. Barabási and P. Pollner for discussions, and B. Kovács and G. Szabó for help with visualization and software support. This research was supported by the Hungarian Research Grant Foundation (OTKA).

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Correspondence to Tamás Vicsek.

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Uncovering the overlapping community structure complex networks in nature and society. Also contains additional references. (PDF 285 kb)

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Palla, G., Derényi, I., Farkas, I. et al. Uncovering the overlapping community structure of complex networks in nature and society. Nature 435, 814–818 (2005).

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