No abstract

Abstract. Existing association rule mining algorithms suffer from many problems when mining massive transactional datasets. One major problem is the high memory dependency: gigantic data structures built are assumed to fit in main memory; in addition, the recursive mining process to mine these structures is also too voracious in memory resources. This paper proposes a new association rule-mining algorithm based on frequent pattern tree data structure. Our algorithm does not use much more memory over and above the memory used by the data structure. For each frequent item, a relatively small independent tree called COFI-tree, is built summarizing co-occurrences. Finally, a simple and non-recursive mining process mines the COFI-trees. Experimental studies reveal that our approach is efficient and allows the mining of larger datasets than those limited by FP-Tree

Regardless of the frequent patterns to discover, either the full frequent patterns or the condensed ones, either closed or maximal, the strategy always includes the traversal of the lattice of candidate patterns. We study the existing depth versus breadth traversal approaches for generating candidate patterns and propose in this paper a new traversal approach that jumps in the search space among only promising nodes. Our leaping approach avoids nodes that would not participate in the answer set and reduce drastically the number of candidate patterns. We use this approach to efficiently pinpoint maximal patterns at the border of the frequent patterns in the lattice and collect enough information in the process to generate all subsequent patterns.

Abstract

The COFI approach for mining frequent itemsets, introduced recently, is an efficient algorithm that was demonstrated to outperform state-of-the-art algorithms on synthetic data. For instance, COFI is not only one order of magnitude faster and requires significantly less memory than the popular FP-Growth, it is also very effective with extremely large datasets, better than any reported algorithm. However, COFI has a significant drawback when mining dense transactional databases which is the case with some real datasets. The algorithm performs poorly in these cases because it ends up generating too many local candidates that are doomed to be infrequent. In this paper, we present a new algorithm COFI* for mining frequent itemsets. This novel algorithm uses the same data structure COFI-tree as its predecessor, but partitions the patterns in such a way to avoid the drawbacks of COFI. Moreover, its approach uses a pseudo-Oracle to pinpoint the maximal itemsets, from which all frequent itemsets are derived and counted, avoiding the generation of candidates fated infrequent. Our implementation tested on real and synthetic data shows that COFI* algorithm outperforms state-of-the-art algorithms, among them COFI itself.