I. Introduction
Social Q&A services are online information-seeking sites offering a method, a place and a community [21], [32]. These sites are variously known by many names [23],[27],[28],[31] and have common features such as a public or semi-public profile, a list of other connected users and a list of connections [7]. The participants' activity in these sites create ties to other users through asking and answering questions, evaluating and ranking the answers and establish a social network [4], [5], [22], [30],[32],[33],[36].