Degree distribution in some non-social collaboration networks

We suggest a notice on the systems, which are not social ones but still can be described by biparticle graph models as well as collaboration networks. As examples, we present real data statistical results about public transportation network in Yangzhou city in 2003, public transportation network in Beijing city in 2003 and the touristy traveling line system in China. We show that, by certain definitions, each transportation or traveling line is described by a complete graph (an act) in the networks. The first system shows a good power-law degree distribution, while the second one shows a nice exponential degree distribution. The third one shows a degree distribution between the two cases: the distribution shows an exponential-like curve in a double-logarithmic plane but with a good linear part (a scaling-free region) in the middle. These results are in very good consistent with their bridge coefficient (how many collaboration acts a node takes part in) distribution. A simplified model that will be presented in another abstract may explain the reason