Reply networks on a bulletin board system

Using data from a bulletin board system (BBS), we constructed reply networks for various boards, which can be considered as social networks connecting people of the same interests. In these networks, identifications (IDs) are treated as nodes and reply articles set up links. We investigated some statistics on these reply networks, such as clustering coefficients, characteristic path lengths, degree distributions, etc., and showed small-world characteristics and scale-free degree distributions of these reply networks. Then we put forward a model of interest space, which is the basis of the reply networks. We indicated that the hierarchical and clustering structure of the interest space, together with overlapping interests of IDs not only result in small-world characteristics of reply networks on BBS, but also give rise to preferential attachment, which is a popular explanation for scale-free features.