RothKS89'

@article{DBLP:journals/acta/RothKS89,
  author    = {Mark A. Roth and
               Henry F. Korth and
               Abraham Silberschatz},
  title     = {Null Values in Nested Relational Databases},
  journal   = {Acta Inf.},
  volume    = {26},
  number    = {7},
  year      = {1989},
  pages     = {615-642},
  ee        = {http://dx.doi.org/10.1007/BF00288974},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}