Networks of companies and branches in Poland
  In this study we consider relations between companies in Poland taking into account common branches they belong to. It is clear that companies belonging to the same branch compete for similar customers, so the market induces correlations between them. On the other hand two branches can be related by companies acting in both of them. To remove weak, accidental links we shall use a concept of threshold filtering for weighted networks where a link weight corresponds to a number of existing connections (common companies or branches) between a pair of nodes. 
Anna M. Chmiel, Julian Sienkiewicz, Krzysztof Suchecki, Janusz A.   Holyst