Cross-document Event Extraction and Tracking: Task, Evaluation, Techniques and Challenges Heng Ji author Ralph Grishman author Zheng Chen author Prashant Gupta author 2009-09 text Proceedings of the International Conference RANLP-2009 Galia Angelova editor Ruslan Mitkov editor Association for Computational Linguistics Borovets, Bulgaria conference publication ji-etal-2009-cross https://aclanthology.org/R09-1032/ 2009-09 166 172