Vianu00c'

@article{DBLP:journals/dr/Vianu00c,
  author    = {Victor Vianu},
  title     = {Review - Exact and Approximate Aggregation in Constraint
               Query},
  journal   = {ACM SIGMOD Digital Review},
  volume    = {2},
  year      = {2000},
  ee        = {db/journals/dr/Vianu00c.html},
  bibsource = {DBLP, http://dblp.uni-trier.de}
}