@inproceedings{DBLP:conf/sigmod/JajodiaS91,
  author    = {Sushil Jajodia and
               Ravi S. Sandhu},
  title     = {Towards a Multilevel Secure Relational Data Model},
  booktitle = {SIGMOD Conference},
  year      = {1991},
  pages     = {50-59},
  ee        = {http://doi.acm.org/10.1145/115790.115796},
  crossref  = {DBLP:conf/sigmod/91, DBLP:conf/sigmod/91},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}

@proceedings{DBLP:conf/sigmod/91,
  editor    = {James Clifford and
               Roger King},
  title     = {Proceedings of the 1991 ACM SIGMOD International Conference
               on Management of Data, Denver, Colorado, May 29-31, 1991},
  publisher = {ACM Press},
  year      = {1991},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}