Over-contribution in discretionary databases

Interest in the study of discretionary databases has grown as numerous large-scale public file-sharing systems have emerged as mainstream internet applications. In particular, much recent work has focused on the free-rider problem in peer-to-peer networks. We examine the related problem of over-contribution in the Usenet file-sharing network, which occurs when a surfeit of contribution causes collective harm. Using a game-theoretic model we show that, first, groups of users can self-regulate their network usage if the users are reputation-motivated, and second, this does not occur on a system-wide level. In the latter case, explicit incentive schemes are needed to motivate behavioural goals.