@INPROCEEDINGS{nss15a-prole15,
  author = {S. Nieva and F. {S\'aenz-P\'erez} and J. S\'anchez},
  title={{HR-SQL: An SQL Database System with Extended Recursion and Hypothetical Reasoning. {\em Ongoing Work}}},
  booktitle={{XV Jornadas sobre Programaci\'on y Lenguajes, PROLE2015
(SISTEDES)}},
  month={September},
  year={2015}
  }