@INPROCEEDINGS{sae11b-prole11,
  author={F. S\'aenz-P\'erez},
  title={{Outer Joins in a Deductive Database System}},
  booktitle={{XI Jornadas sobre Programaci\'on y Lenguajes, PROLE2011
(SISTEDES)}},
  month={September},
  year={2011}
  }