@inproceedings{xu2013filling,
  title={Filling knowledge base gaps for distant supervision of relation extraction},
  author={Xu, Wei and Le, Zhao and Hoffmann, Raphael and Grishman, Ralph},
  booktitle = {Proceedings of the 2013 Conference of the Association for Computational Linguistics (ACL 2013)},
  month     = {July},
  year      = {2013},
  address   = {Sofia, Bulgaria},
  publisher = {Association for Computational Linguistics},
  url = {http://aclweb.org/anthology/P/P13/P13-2117.pdf}
}