Alejandro P. Buchmann Ming-Chuan Wu Supporting Group-By and Pipelining in Bitmap-Enabled Query Processors. 249-260 http://dx.doi.org/10.1007/3-540-47849-3_14 1999 conf/sofsem/1999 SOFSEM db/conf/sofsem/sofsem1999.html#BuchmannW99