  Inter-firm organizations, which play a driving role in the economy of a
country, can be represented in the form of a customer-supplier network. Such a
network exhibits a heavy-tailed degree distribution, disassortative mixing and
a prominent community structure. We analyze a large-scale data set of
customer-supplier relationships containing data from one million Japanese
firms. Using a directed network framework, we show that the production network
exhibits the characteristics listed above. We conduct detailed investigations
to characterize the communities in the network. The topology within smaller
communities is found to be very close to a tree-like structure but becomes
denser as the community size increases. A large fraction (~40%) of firms with
relatively small in- or out-degrees have customers or suppliers solely from
within their own communities, indicating interactions of a highly local nature.
The interaction strengths between communities as measured by the
inter-community link weights follow a highly heterogeneous distribution. We
further present the statistically significant over-expressions of different
prefectures and sectors within different communities.
