More Data, More Relations, More Context and More Openness: A Review and Outlook for Relation Extraction. - Xu Han 007; Tianyu Gao 001; Yankai Lin; Hao Peng 015; Yaoliang Yang; Chaojun Xiao; Zhiyuan Liu 001; Peng Li 030; Jie Zhou 016; Maosong Sun 001 (AACL/IJCNLP, 2020)