Association Rule Mining (II).ppt

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1、Association Rule Mining (II),Instructor: Qiang Yang Thanks: J.Han and J. Pei,Frequent-pattern mining methods,2,Bottleneck of Frequent-pattern Mining,Multiple database scans are costly Mining long patterns needs many passes of scanning and generates lots of candidates To find frequent itemset i1i2i10

2、0 # of scans: 100 # of Candidates: (1001) + (1002) + + (110000) = 2100-1 = 1.27*1030 ! Bottleneck: candidate-generation-and-test Can we avoid candidate generation?,Frequent-pattern mining methods,3,FP-growth: Frequent-pattern Mining Without Candidate Generation,Heuristic: let P be a frequent itemset

3、, S be the set of transactions contain P, and x be an item. If x is a frequent item in S, x P must be a frequent itemset No candidate generation! A compact data structure, FP-tree, to store information for frequent pattern mining Recursive mining algorithm for mining complete set of frequent pattern

4、s,Frequent-pattern mining methods,4,Example,Min Support = 3,Frequent-pattern mining methods,5,Scan the database,List of frequent items, sorted: (item:support)The root of the tree is created and labeled with “” Scan the database Scanning the first transaction leads to the first branch of the tree: Or

5、der according to frequency,Frequent-pattern mining methods,6,Scanning TID=100,Transaction Database TID Items 100 f,a,c,d,g,i,m,p,f:1,c:1,a:1,m:1,p:1,Header TableNode Item count head f 1 c 1 a 1m 1p 1,root,Frequent-pattern mining methods,7,Scanning TID=200,Frequent Single Items: F1= TID=200 Possible

6、frequent items: Intersect with F1: f,c,a,b,m Along the first branch of , intersect: Generate two children , ,Frequent-pattern mining methods,8,Scanning TID=200,Transaction Database TID Items 200 f,c,a,b,m,f:2,c:2,a:2,m:1,p:1,Header TableNode Item count head f 1 c 1 a 1 b 1 m 2p 1,root,b:1,m:1,Freque

7、nt-pattern mining methods,9,The final FP-tree,Transaction Database TID Items 100 f,a,c,d,g,i,m,p 200 a,b,c,f,l,m,o 300 b,f,h,j,o 400 b,c,k,s,p 500 a,f,c,e,l,p,m,n Min support = 3,Frequent 1-items in frequency descending order:f,c,a,b,m,p,f:4,c:1,b:1,p:1,b:1,c:3,a:3,b:1,m:2,p:2,m:1,Header TableNode I

8、tem count head f 1 c 2 a 1 b 3 m 2 p 2,Frequent-pattern mining methods,10,FP-Tree Construction,Scans the database only twice Subsequent mining: based on the FP-tree,Frequent-pattern mining methods,11,How to Mine an FP-tree?,Step 1: form conditional pattern base Step 2: construct conditional FP-tree

9、Step 3: recursively mine conditional FP-trees,Frequent-pattern mining methods,12,Conditional Pattern Base,Let I be a frequent item A sub database which consists of the set of prefix paths in the FP-tree With item I as a co-occurring suffix pattern Example: m is a frequent item ms conditional pattern

10、 base: : support =2 : support = 1 Mine recursively on such databases,f:4,c:1,b:1,p:1,b:1,c:3,a:3,b:1,m:2,p:2,m:1,Frequent-pattern mining methods,13,Conditional Pattern Tree,Let I be a suffix item, DB|I be the conditional pattern base The frequent pattern tree TreeI is known as the conditional patter

11、n tree Example: m is a frequent item ms conditional pattern base: : support =2 : support = 1 ms conditional pattern tree,f:4,c:3,a:3,m:2,Frequent-pattern mining methods,14,Composition of patterns a and b,Let a be a frequent item in DB, B be as conditional pattern base, and b be an itemset in B. Then

12、 a + b is frequent in DB if and only if b is frequent in B. Example: Starting with a=p ps conditional pattern base (from the tree) B= (f,c,a,m): 2 (c,b): 1 Let b be c. Then a+b=p,c, with support = 3.,Frequent-pattern mining methods,15,Single path tree,Let P be a single path FP tree Let I1, I2, Ik be

13、 an itemset in the tree Let Ij have the lowest support Then the support(I1, I2, Ik)=support(Ij) Example:,f:4,c:1,b:1,p:1,b:1,c:3,a:3,b:1,m:2,p:2,m:1,Frequent-pattern mining methods,16,FP_growth Algorithm Fig 6.10,Recursive Algorithm Input: A transaction database, min_supp Output: The complete set of

14、 frequent patterns 1. FP-Tree construction 2. Mining FP-Tree by calling FP_growth(FP_tree, null) Key Idea: consider single path FP-tree and multi-path FP-tree separately Continue to split until get single-path FP-tree,Frequent-pattern mining methods,17,FP_Growth (tree, a),If tree contains a single p

15、ath P, then For each combination (denoted as b) of the nodes in the path P, then Generate pattern b+a with support = min_supp of nodes in b Else for each a in the header of tree, do Generate pattern b = a + a with support = a.support; Construct (1) bs conditional pattern base and (2) bs conditional

16、FP-tree Treeb If Treeb is not empty, then Call FP-growth(Treeb, b); ,Frequent-pattern mining methods,18,FP-Growth vs. Apriori: Scalability With the Support Threshold,Data set T25I20D10K,Frequent-pattern mining methods,19,FP-Growth vs. Tree-Projection: Scalability with the Support Threshold,Data set

17、T25I20D100K,Frequent-pattern mining methods,20,Why Is FP-Growth the Winner?,Divide-and-conquer: decompose both the mining task and DB according to the frequent patterns obtained so far leads to focused search of smaller databases Other factors no candidate generation, no candidate test compressed da

18、tabase: FP-tree structure no repeated scan of entire database basic opscounting and FP-tree building, not pattern search and matching,Frequent-pattern mining methods,21,Implications of the Methodology: Papers by Han, et al.,Mining closed frequent itemsets and max-patterns CLOSET (DMKD00) Mining sequ

19、ential patterns FreeSpan (KDD00), PrefixSpan (ICDE01) Constraint-based mining of frequent patterns Convertible constraints (KDD00, ICDE01) Computing iceberg data cubes with complex measures H-tree and H-cubing algorithm (SIGMOD01),Frequent-pattern mining methods,22,Visualization of Association Rules

20、: Pane Graph,Frequent-pattern mining methods,23,Visualization of Association Rules: Rule Graph,Frequent-pattern mining methods,24,Mining Various Kinds of Rules or Regularities,Multi-level, quantitative association rules, correlation and causality, ratio rules, sequential patterns, emerging patterns,

21、 temporal associations, partial periodicity Classification, clustering, iceberg cubes, etc.,Frequent-pattern mining methods,25,Multiple-level Association Rules,Items often form hierarchy Flexible support settings: Items at the lower level are expected to have lower support. Transaction database can

22、be encoded based on dimensions and levels explore shared multi-level mining,Frequent-pattern mining methods,26,Quantitative Association Rules,age(X,”34-35”) income(X,”30K - 50K”) buys(X,”high resolution TV”),Numeric attributes are dynamically discretized Such that the confidence or compactness of th

23、e rules mined is maximized. 2-D quantitative association rules: Aquan1 Aquan2 Acat Cluster “adjacent” association rules to form general rules using a 2-D grid. Example:,Frequent-pattern mining methods,27,Redundant Rules SA95,Which rule is redundant? milk wheat bread, support = 8%, confidence = 70% “

24、skim milk” wheat bread, support = 2%, confidence = 72% The first rule is more general than the second rule. A rule is redundant if its support is close to the “expected” value, based on a general rule, and its confidence is close to that of the general rule.,INCREMENTAL MINING CHNW96,Rules in DB wer

25、e found and a set of new tuples db is added to DB, Task: to find new rules in DB + db. Usually, DB is much larger than db. Properties of Itemsets: frequent in DB + db if frequent in both DB and db. infrequent in DB + db if also in both DB and db. frequent only in DB, then merge with counts in db. No

26、 DB scan is needed! frequent only in db, then scan DB once to update their itemset counts. Same principle applicable to distributed/parallel mining.,Frequent-pattern mining methods,29,CORRELATION RULES,Association does not measure correlation BMS97, AY98. Among 5000 students 3000 play basketball, 37

27、50 eat cereal, 2000 do both play basketball eat cereal 40%, 66.7% Conclusion: “basketball and cereal are correlated” is misleading because the overall percentage of students eating cereal is 75%, higher than 66.7%. Confidence does not always give correct picture!,Frequent-pattern mining methods,30,C

28、orrelation Rules,P(AB)=P(B)*P(A), if A and B are independent events A and B negatively correlated the value is less than 1; Otherwise A and B positively correlated.,P(B|A)/P(B) is known as the lift of rule BA If less than one, then B and A are negatively correlated. BasketballCereal 2000/(3000*3750/

29、5000)=2000*5000/3000*37501,Frequent-pattern mining methods,31,Chi-square Correlation BMS97,The cutoff value at 95% significance level is 3.84 0.9 Thus, we do not reject the independence assumption.,Frequent-pattern mining methods,32,Constraint-based Data Mining,Finding all the patterns in a database

30、 autonomously? unrealistic! The patterns could be too many but not focused! Data mining should be an interactive process User directs what to be mined using a data mining query language (or a graphical user interface) Constraint-based mining User flexibility: provides constraints on what to be mined

31、 System optimization: explores such constraints for efficient miningconstraint-based mining,Frequent-pattern mining methods,33,Constraints in Data Mining,Knowledge type constraint: classification, association, etc. Data constraint using SQL-like queries find product pairs sold together in stores in

32、Vancouver in Dec.00 Dimension/level constraint in relevance to region, price, brand, customer category Rule (or pattern) constraint small sales (price $200) Interestingness constraint strong rules: min_support 3%, min_confidence 60%,Frequent-pattern mining methods,34,Constrained Mining vs. Constrain

33、t-Based Search,Constrained mining vs. constraint-based search/reasoning Both are aimed at reducing search space Finding all patterns satisfying constraints vs. finding some (or one) answer in constraint-based search in AI Constraint-pushing vs. heuristic search It is an interesting research problem

34、on how to integrate them Constrained mining vs. query processing in DBMS Database query processing requires to find all Constrained pattern mining shares a similar philosophy as pushing selections deeply in query processing,Frequent-pattern mining methods,35,Constrained Frequent Pattern Mining: A Mi

35、ning Query Optimization Problem,Given a frequent pattern mining query with a set of constraints C, the algorithm should be sound: it only finds frequent sets that satisfy the given constraints C complete: all frequent sets satisfying the given constraints C are found A nave solution First find all f

36、requent sets, and then test them for constraint satisfaction More efficient approaches: Analyze the properties of constraints comprehensively Push them as deeply as possible inside the frequent pattern computation.,Frequent-pattern mining methods,36,Anti-Monotonicity in Constraint-Based Mining,Anti-

37、monotonicity intemset S satisfies the constraint, so does any of its subset sum(S.Price) v is anti-monotone sum(S.Price) v is not anti-monotone Example. C: range(S.profit) 15 is anti-monotone Itemset ab violates C So does every superset of ab,TDB (min_sup=2),Frequent-pattern mining methods,37,Which

38、Constraints Are Anti-Monotone?,Frequent-pattern mining methods,38,Monotonicity in Constraint-Based Mining,Monotonicity When an intemset S satisfies the constraint, so does any of its superset sum(S.Price) v is monotone min(S.Price) v is monotone Example. C: range(S.profit) 15 Itemset ab satisfies C

39、So does every superset of ab,TDB (min_sup=2),Frequent-pattern mining methods,39,Which Constraints Are Monotone?,Frequent-pattern mining methods,40,Succinctness, Convertible, Inconvertable Constraints in Book,We will not consider these in this course.,Frequent-pattern mining methods,41,Associative Cl

40、assification,Mine association possible rules in form of itemset class Itemset: a set of attribute-value pairs Class: class label Build Classifier Organize rules according to decreasing precedence based on confidence and support B. Liu, W. Hsu & Y. Ma. Integrating classification and association rule

41、mining. In KDD98,Frequent-pattern mining methods,42,Classification by Aggregating Emerging Patterns,Emerging pattern (EP): A pattern frequent in one class of data but infrequent in others. Age=30 is frequent in class “buys_computer=yes” and infrequent in class “buys_computer=no” Rule: age=30 buys computer G. Dong & J. Li. Efficient mining of emerging patterns: discovering trends and differences. In KDD99,