An efficient algorithm for mining both closed and maximal frequent free subtrees using canonical forms

A large number of text files, including HTML documents and XML documents, can be organized as tree structures. One objective of data mining is to discover frequent patterns in them. In this paper, first, we introduce a canonical form of free tree, which is based on the breadth-first canonical string; secondly, we present some properties of a closed frequent subtree and a maximal frequent subtree as well as their relationships; thirdly, we study a pruning technique of frequent free subtree and improvement on the mining of the nonclosed frequent free subtree; finally, we present an algorithm that mines all closed and maximal frequent free trees and prove validity of this algorithm.