The rollup and the drilldown are quite frequent based on dimension hierarchies in on-line analytical processing （OLAP）, but prefixCube does not directly support dimension hierarchies. The PrefixCube is extended for incorporating hierarchical data cubes, i.e. cubes with hierarchical dimensions ,thus obtaining HierPrefixCube. HierPrefixCube retains advantages on computation and organization of PrefixCube, and it can directly support aggregate queries on levels of the dimension hierarchy.
A novel association-based algorithm EmailinClass is proposed for incremental Email classification. In view of the fact that the basic semantic unit in an Email is actually a sentence, and the words within the same sentence are typically more semantically related than the words that just appear in the same Email, EmailInClass views a sentence rather than an Email as a transaction. Extensive experiments conducted on benchmark corpora Enron reveal that the effectiveness of EmallInClass is superior to the non-incremental alternatives such as NalveBayes and SAT-MOD. In addition, the classification rules generated by EroaillnClass are human readable and revisable,
