Bipartite network projection
Bipartite network projection is an extensively used method for compressing information about bipartite networks. Since the one-mode projection is always less informative than the original bipartite graph, an appropriate method for weighting network connections is often required. Optimal weighting methods reflect the nature of the specific network, conform to the designer's objectives and aim at minimizing information loss. Background. Bipartite networks are a particular class of complex networks, whose nodes are divided into two sets X and Y, and only connections between two nodes in different sets are allowed. For the convenience of directly showing  the relation structure among a particular set of nodes, bipartite networks are usually compressed by one-mode projection. This means that the ensuing network contains nodes of only either of the two sets, and two X (or, alternatively, Y) nodes are connected only when they have at least one common neighboring Y (or, alternatively, X) node. The simplest method involves projecting the bipartite network onto an unweighted network, without taking into account the topology of the network or the frequency of sharing a connection to the elements of the opposing set. Since bipartite networks with largely different structures can have  exactly the same one-mode representation in this case, a lucid illustration of the original network topology usually requires the use of some weighting method. Possible weighting methods. According to the designer's needs and the topological properties of the given network, several different weighting methods have been proposed. Since the redistribution of weights is found to have a strong effect on the community structure (especially in dense networks), the methodological choice must be made with care.