@conference {550, title = {DS4: A Distributed Social and Semantic Search System}, booktitle = {Proceedings of 35th European Conference on Information Retrieval (ECIR)}, year = {2013}, month = {March}, address = {Moscow, Russia}, author = {Dionisis Kontominas and Paraskevi Raftopoulou and Christos Tryfonopoulos and E.G.M. Petrakis} }