1. CanTree: a tree structure for efficient incremental mining of frequent patterns Carson Kai-Sang Leung, Quamrul I. Khan, Tariqul Hoque ICDM ’ 05 報告者：林靜怡 2006/11/15

2. Introduction Many existing incremental mining algorithms are Apriori-based not easily adoptable to FP-tree based frequent-pattern mining

3. Related Work The FELINE Algorithm with the CATS Tree The AFPIM Algorithm

4. The FELINE Algorithm with the CATS Tree CATS tree (Compressed and Arranged Transaction Sequences tree)  Allows frequent-pattern mining without the generation of candidate itemsets  requires one database scan to build the tree

5. CATS Tree New transactions are added at the root level At each level, items of the new transaction are compared with children (or descendant) nodes.  If the same items exist in both 1.the transaction is merged with the node at the highest frequency level 2.The remainder of the transaction is then added to the merged nodes repeated recursively until all common items are found.

6. CATS Tree Any remaining items of the transaction are added as a new branch to the last merged node. The frequency of a node is lower than or equal to the frequencies of its ancestors If the frequency of a node becomes higher than its ancestors, then it has to swap with the ancestors

8. Weaknesses tree construction could be computationally expensive checks existing tree paths one-by-one until a mergeable one is found extra cost is required for the swapping or merging of nodes.

9. The AFPIM Algorithm Adjusting FP-tree for Incremental Mining all the “ frequent ” items are arranged in descending order of their global frequency when the ordering is changed, items in the tree need to be adjusted When previously infrequent item becomes “ frequent ” in the updated database, it needs to rescan and build a new FP-tree.

10. preMinsup:35% minsup:55% 4 x 0.35 = 1.4

11. Weaknesses the amount of computation spent on swapping, merging, and splitting tree nodes requirement for an additional mining parameter preMinsup  finding an appropriate value for this parameter is not easy

12. Weaknesses when the database is updated, item frequencies may have changed. This results in changes in the ordering. Both FELINE and AFPIM algorithms need lots of swapping, merging, and splitting of tree nodes

13. Canonical-Order Tree (CanTree) requires one database scan items are arranged according to some canonical order  in lexicographic order or alphabeticalorder  some specific order depending on the item properties

14. Property Property 1 The ordering of items is unaffected by the changes in frequency caused by incremental updates. Property 2 The frequency of a node in the CanTree is at least as high as the sum of frequencies of its children.

15. CanTree Transactions can be easily added to the CanTree without any extensive searches for mergeable paths mine frequent patterns from the tree in a fashion similar to FP-growth(a divide- and-conquer approach).

16. g: eg,deg,cdeg,bcdeg,abcdeg e: de,cde,bcde,abcde,ce, bce,abce,de,bde,abde f: ef,def,bdef,abdef d: cd,bcd,abcd,bd,abd c: bc,abc b: ab

17. Discussion CanTrees can be used for incremental constrained mining Efficiency and Memory Issues  On the surface, it appears CanTree may take a large amount of memory.  CanTree may not be as compact as the CATS tree,but it significantly reduce computation and time  assume we have enough main memory space

18. Experiment Database:generated by the program developed at IBM Almaden Research Center consists of 1M records with an average transaction length of 10 items and a domain of 1000 items time-sharing environment in a 1 GHz machine

19. Experiment

23. Conclusion provide the user with a simple, but powerful, tree structure for efficient FP- tree based incremental mining CanTree can be easily maintained Can used for efficient incremental constrained mining