@article{journals/tois/GottlobSR96,
  title = "Extending Object-Oriented Systems with Roles",
  author = "Georg Gottlob and Michael Schrefl and Brigitte R{\"o}ck",
  year = "1996",
  journal = "{ACM Trans. Inf. Syst.}",
  number = "3",
  pages = "268-296",
  volume = "14",
  doi = "10.1145/230538.230540",
}