Recent research suggests that clustering for high-dimensional data should involve searching for "hidden" subspaces with lower dimensionalities, in which patterns can be observed when data objects are projected onto the subspaces. Discovering such interattribute correlations and location of the corresponding clusters is known as the projective clustering problem. We propose an efficient projective clustering technique by histogram construction (EPCH). The histograms help to generate "signatures", where a signature corresponds to some region in some subspace, and signatures with a large number of data objects are identified as the regions for subspace clusters. Hence, projected clusters and their corresponding subspaces can be uncovered. Compared to the best previous methods to our knowledge, this approach is more flexible in that less prior knowledge on the data set is required, and it is also much more efficient. Our experiments compare behaviors and performances of this approach and other projective clustering algorithms with different data characteristics. The results show that our technique is scalable to very large databases, and it is able to return accurate clustering results.

With high-dimensional data, natural clusters are expected to exist in different subspaces. We propose the EPC (efficient projected clustering) algorithm to discover the sets of correlated dimensions and the location of the clusters. This algorithm is quite different from previous approaches and has the following advantages: (1) there is no requirement on the input regarding the number of natural clusters and the average cardinality of the subspaces; (2) it can handle clusters of irregular shapes; (3) it produces better clustering results compared to the best previous method; (4) it has high scalability. From experiments, it is several times faster than the previous method, while producing more accurate results.

Association rule mining is an important data mining problem. It is found to be useful for conventional relational data. However, previous work has mostly targeted on mining a single table. In real life, a database is typically made up of multiple tables and one important case is where some of the tables form a star schema. The tables typically correspond to entity sets and joining the tables in a star schema gives relationships among entity sets which can be very interesting information. Hence mining on the join result is an important problem. Based on characteristics of the star schema we propose an efficient algorithm for mining association rules on the join result but without actually performing the join operation. We show that this approach can significantly out-perform the join-then-mine approach even when the latter adopts a fastest known mining algorithm.