title: Growing network model for community with group structure.
abstract: We propose a growing network model for a community with a group structure. The community consists of individual members and groups, gatherings of members. The community grows as a new member is introduced by an existing member at each time step. The new member then creates a new group or joins one of the groups of the introducer. We investigate the emerging community structure analytically and numerically. The group size distribution shows a power-law distribution for a variety of growth rules, while the activity distribution follows an exponential or a power law depending on the details of the growth rule. We also present an analysis of empirical data from online communities the "Groups" in http://www.yahoo.com and the "Cafe" in http://www.daum.net, which show a power-law distribution for a wide range of group sizes.
authors.affiliation: Department of Physics, Chungnam National University, Daejeon 305-764, Korea.
authors.forename: Jae Dong
authors.initials: JD
authors.lastname: Noh
authors.forename: Hyeong-Chai
authors.initials: HC
authors.lastname: Jeong
authors.forename: Yong-Yeol
authors.initials: YY
authors.lastname: Ahn
authors.forename: Hawoong
authors.initials: H
authors.lastname: Jeong