  In this paper, we analyse the sustainability of social networks using STrust,
our social trust model. The novelty of the model is that it introduces the
concept of engagement trust and combines it with the popularity trust to derive
the social trust of the community as well as of individual members in the
community. This enables the recommender system to use these different types of
trust to recommend different things to the community, and identify (and
recommend) different roles. For example, it recommends mentors using the
engagement trust and leaders using the popularity trust. We then show the
utility of the model by analysing data from two types of social networks. We
also study the sustainability of a community through our social trust model. We
observe that a 5% drop in highly trusted members causes more than a 50% drop in
social capital that, in turn, raises the question of sustainability of the
community. We report our analysis and its results.
