Compariso no fOnlin eSocia lRelation si nTerm sof Volume vs. Interaction: A Case Study of Cyworld

Online social networking services are among the most popular In- ternet services according to Alexa.com and have become a key fea- ture in many Internet services. Users interact through various fea- tures of online social networking services: making friend relation- ships, sharing their photos, and writing comments. These friend re- lationships are expected to become a key to many other features in web services, such as recommendation engines, security measures, online search, and personalization issues. However, we have very limited knowledge on how much interaction actually takes place over friend relationships declared online. A friend relationship only marks the beginning of online interaction. Does the interaction between users follow the declaration of friend relationship? Does a user interact evenly or lopsidedly with friends? We venture to answer these questions in this work. We construct a network from comments written in guestbooks. A node represents a user and a directed edge a comments from a user to another. We call this network an activity network. Previous work on activity networks include phone-call networks (34, 35) and MSN messen- ger networks (27). To our best knowledge, this is the first attempt to compare the explicit friend relationship network and implicit ac- tivity network. We have analyzed structural characteristics of the activity net- work and compared them with the friends network. Though the activity network is weighted and directed, its structure is similar to the friend relationship network. We report that the in-degree and out-degree distributions are close to each other and the social in- teraction through the guestbook is highly reciprocated. When we consider only those links in the activity network that are recipro- cated, the degree correlation distribution exhibits much more pro- nounced assortativity than the friends network and places it close to known social networks. The k-core analysis gives yet another This work was conducted while Ahn was at KAIST.