Hierarchical structure of network discovered

Published in the Nature journal, the work from a group a researcher from Santa Fe Institute (SFI) reveals that for a complex network, there is an underlying hierarchical structure regarding the connectivity among nodes.  Graph cluster could be one form of hierarchical network, where small clusters make up a bigger ones that make up the network. The same can be said for modules in biochemical networks or communities in social networks. 

The full paper, which can be found here, is quite long to read. Basically, the hierarchy in the network can be represented by a (probabilistic) tree. The details are not yet very clear for me. Results from the paper say that the construction of such tree can be automated, impact of which can be very significant. First of all, given incomplete data from a network, one can reconstruct the missing links with high accuracy. Secondly, this can be another way to construct popular type of networks such as power-law or small-world.