Data Science and Big Data: An Environment of Computational Intelligence by Witold Pedrycz & Shyi-Ming Chen

Author:Witold Pedrycz & Shyi-Ming Chen
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

(5)

The closed twu itemset X obtained by the intersection of each closed twu itemset Y with Cid in SET({TADD}) and TADD need to be updated when a transaction TADD is added. The closed twu itemsets which need to be updated after adding transaction TADD are recorded in the table TempADD, which includes the two fields: UItemset records the closed twu itemset X which needs to be updated; Closure_Id records the Cid of the closure of X before adding transaction TADD, that is, the Cid of itemset Y. If there is the same closed twu itemset X generated by the intersections of different closed twu itemsets and TADD, then the closure of X is the closed twu itemset with the largest twu value among the different closed twu itemsets. Because an added transaction TADD must be a closed twu itemset [20], TADD is recorded in TempADD and the corresponding Closure_Id is set to be 0, which represents that we cannot know the closure of TADD before adding the transaction so far. HUIStream can update the content of Closed Table according to the TempADD.

For each record in TempADD, HUIStream compares the itemset X in UItemset and the itemset Y with Cid in Closure_Id. If X and Y are the same, that is, X is a closed twu itemset before adding the transaction TADD, then the utility of each item in X is increased by adding the utility of the item in TADD, and the twu of X is increased by adding the tu of TADD. If X and Y are different, that is, X is not a closed twu itemset before adding the transaction TADD and turns out to be a closed twu itemset after adding the transaction, then HUIStream assigns X a unique Cid and adds it into The Closed Table and Cid List, in which the twu of X is the twu of Y plus the tu of TADD and the utility of each item is the utility of the item in Y in Closed Table plus the utility of the item in TADD, since the twu of X is equal to the twu of Y before adding the transaction TADD.

If itemset X is not a closed HTWU itemset before adding transaction TADD, but is closed HTWU itemsets after adding the transaction, then the Equal TWU itemsets of the Closure Y of X becomes the Equal TWU itemsets of X. If the Closure of X is not a closed HTWU Itemset, then the Equal TWU itmesets of X are the subsets of X, which have the same twu as X. HUIStream uses the following method to determine if the subset Z of X is an Equal TWU itemset of X: If the twu of X is the largest twu among all the itemsets with Cids in SET(Z) according to expression (5), then Z is an Equal TWU itemset of X, that is, X is the Closure of Z. If X is a closed twu itemset before adding the transaction, then HUIStream only needs to justify if X is a closed HTWU itemset after adding the transaction.

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