Activity Network (vs. Social Network) and its Evolution in Facebook

Recently, researchers have suggested examining the activity network—a network that is based on the actual interaction between users, rather than mere friendship—to distinguish between strong and weak links.

Initial studies have led to insights on how an activity network is structurally different from the social network itself.

A natural and important aspect of the activity network: whether social links can grow stronger or weaker over time.

In the study of the evolution of activity between users in the Facebook social network, it is found that links in the activity network tend to come and go rapidly over time, and the strength of ties exhibits a general decreasing trend of activity as the social network link ages. For example, only 30% of Facebook user pairs interact consistently from one month to the next. Interestingly, even though the links of the activity network change rapidly over time, many graph-theoretic properties of the activity network remain unchanged.

Interactions between pairs of users who interact infrequently are likely triggered by site mechanisms. For example, over 54% of the interactions between the infrequently interacting user pairs can be directly attributed to Facebook’s birthday reminder feature, which implies that the mechanisms present on the online social networking sites can affect the activity network in unexpected ways.

Even when users do interact frequently, the activity level of user pairs tends to decrease markedly over time, implying that most activity links die out. However, highly active user pairs exhibit this trend to a lesser degree, further emphasizing the strength of these links.

Surprisingly, while the individual user pairs that compose the activity network changes rapidly over time (i.e., over the course of one month 70% of the links in the activity network disappear), many of the graph-theoretic properties (e.g., average node degree, average clustering coefficient, average path length) show remarkable stability over the course of two years.

From Bimal Viswanath, Alan Mislove, Meeyoung Cha, Krishna P. Gummadi, On the Evolution of User Interaction in Facebook,Proceedings of the 2nd ACM SIGCOMM Workshop On Social Networks (WOSN), Barcelona, Spain, August 2009. http://www.mpi-sws.org/~gummadi/papers/wosn23-viswanath.pdf

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About Kyoung Jun Lee
Professor of Kyung Hee Univ.

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