@inproceedings{zhu2015tackling,
  title={Tackling Data Sparseness in Recommendation using Social Media based Topic Hierarchy Modeling.},
  author={Zhu, Xingwei and Ming, Zhaoyan and Hao, Yu and Zhu, Xiaoyan},
  booktitle={IJCAI},
  pages={2415--2423},
  year={2015}
}