H. Purohit, Y. Ruan, A. Joshi, S. Parthasarathy, A. Sheth. Understanding User-Community Engagement by Multi-faceted Features: A Case Study on Twitter. in SoME 2011 (Workshop on Social Media Engagement, in conjunction with WWW 2011), March 29, 2011. Paper: http://knoesis.org/library/resource.php?id=1095 More on Social Media @ Kno.e.sis at http://knoesis.org/research/semweb/projects/socialmedia/