% One entry per reference. The key is what you pass to \cite.
@inproceedings{sadowski2015,
  author    = {Caitlin Sadowski and Kathryn T. Stolee and Sebastian Elbaum},
  title     = {How developers search for code: a case study},
  booktitle = {Proceedings of the Symposium on the Foundations of Software Engineering},
  series    = {FSE 2015},
  pages     = {191-201},
  publisher = {ACM},
  address   = {New York, NY, USA},
  year      = {2015}
}

@article{xia2017,
  author  = {Xin Xia and Lingfeng Bao and David Lo and Pavneet Singh Kochhar},
  title   = {What do developers search for on the web},
  journal = {Empirical Software Engineering},
  volume  = {22},
  number  = {6},
  pages   = {3149-3185},
  year    = {2017}
}