Yannis Sismanis Antonios Deligiannakis Yannis Kotidis Nick Roussopoulos Hierarchical dwarfs for the rollup cube. 17-24 2003 conf/dolap/2003 DOLAP http://doi.acm.org/10.1145/956060.956064 db/conf/dolap/dolap2003.html#SismanisDKR03