Flexible Query Answering Systems 13th International Conference, FQAS 2019, Amantea, Italy, July 2-5, 2019, Proceedings - Cuzzocrea, Alfredo; Cuzzocrea, Alfredo; Greco, Sergio; Greco, Sergio; Larsen, Henrik Legind; Larsen, Henrik Legind; Saccà, Domenico; Saccà, Domenico; Andreasen, Troels; Andreasen, Troels; Christiansen, Henning; Christiansen, Henning (Springer International Publishing : Imprint: Springer, 2019)