531 � � � � Technical Papers SNS – mixi – How Relations are Built within a SNS World – Social Network Anal- ysis on Mixi – Yutaka Matsuo / National Institute of Advanced Science and Technology / Stanford University y.matsuo@aist.go.jp, http://ymatsuo.com/ Yuki Yasud The University of Tokyo, Graduate School of Economics yasuda@mmrc.e.u-tokyo.ac.jp keywords: social networking service, community, soc