Advances in information retrieval 41st European Conference on IR Research, ECIR 2019, Cologne, Germany, April 14-18, 2019, proceedings, part II - Azzopardi, Leif; Stein, Benno; Fuhr, Norbert 1956-; Mayr, Philipp; Hauff, Claudia; Hiemstra, Djoerd (Springer, 2019)