@article{DBLP:journals/tods/LockemannMWW79,
  author    = {Peter C. Lockemann and
               Heinrich C. Mayr and
               Wolfgang H. Weil and
               Wolfgang H. Wohlleber},
  title     = {Data Abstractions for Database Systems},
  journal   = {ACM Trans. Database Syst.},
  volume    = {4},
  number    = {1},
  year      = {1979},
  pages     = {60-75},
  ee        = {http://doi.acm.org/10.1145/320064.320067},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}