Frequent patterns are useful in many data mining problems including query suggestion. Frequent patterns can be mined through frequent pattern tree (FP-tree) data structure which is used to store the compact (or compressed) representation of a transaction database (Han, et al, 2000). In this paper, we propose an algorithm to o press frequent pattern set into a smaller one, and store the set in a modified version of FP-tree (called compact FP-tree) as an inverted indexing of patterns for later quick retrieval (for query suggestion). With the compact FP-tree, we can also restore the original frequent pattern set. Our experiment results show that our compact FP-tree has a very good compression ratio, especially on sparse dataset which is the nature of query log.
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