Research and advanced technology for digital libraries 21st International Conference on Theory and Practice of Digital Libraries, TPDL 2017, Thessaloniki, Greece, September 18-21, 2017 : proceedings - Kamps, Jacob; Tsakonas, Giannis; Manolopoulos, Yannis 1957-; Iliadis, Lazaros; Karydis, Ioannis (Lecture Notes in Computer Science, 2017)