Indexing Evolving Databases for Itemset Mining

Research activity in data mining has been initially focused on defining efficient algorithms to perform the computationally intensive knowledge extraction task (i.e., itemset mining). The data to be analyzed was (possibly) extracted from the DBMS and stored into binary files. Proposed approaches for mining flat file data require a lot of memory and do not scale efficiently on large databases. An improved memory management could be achieved through the integration of the data mining algorithm into the kernel of the database management system. Furthermore, most data mining algorithms deal with “static” datasets (i.e., datasets which do not change over time). This chapter presents a novel index, called I-Forest, to support data mining activities on evolving databases, whose content is periodically updated through insertion (or deletion) of data blocks. I-Forest is a covering index that represents transactional blocks in a succinct form and allows different kinds of analysis. Time and support constraints (e.g., “analyze frequent quarterly data”) may be enforced during the extraction phase. The I-Forest index has been implemented into the PostgreSQL open source DBMS and it exploits its physical level access methods. Experiments, run for both sparse and dense data distributions, show the efficiency of the proposed approach which is always comparable with, and for low support threshold faster than, the Prefix-Tree algorithm accessing static data on flat file.