1 mining association rules with constraints wei ning joon wong cosc 6412 presentation

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Mining Association Rules with Constraints

Wei NingJoon Wong

COSC 6412 Presentation

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Outline Introduction Summary of Approach Algorithm CAP Performance Analysis Conclusion References

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Introduction Recall mining association rules

Association rules mining finds interesting association or correlation relationships among a large set of data items.

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Some problems we met during mining association rules Overwhelming? Not what you want? Wait so long? Lack of Focus

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Introduction(cont.) Example in walmart Suppose a manager want to find

which is the most popular shoes in winter?

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Mining frequent itemsets vs. Mining association rules Mining frequent itemsets is almost

the same as Mining association rules

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Constrained Mining A naive solution

First find all frequent sets, and then test them for constraint satisfaction

Our approach:Analyze the properties of constraints comprehensively Push them as deeply as possible inside the frequent pattern computation.

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Frequent Itemsets & Constraints

Given a transaction database

Frequent itemset: a subset of items frequently appear in transactions, e.g. {a, c}

Constraint: a predicate over itemsets C(I): sum(I)>50 C(abd)=

TransactionTID

a, b, c10b, c, d, f20

a, c30

TDB (min_sup=2)

Item

Value

a 40b 10c -20d 10e -30

true

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Mining Frequent Itemsets With Constraints Given

A transaction database TDB A support threshold min_sup A constraint C

Find the complete set of frequent itemsets satisfying the constraint

Use constraint to Express user’s focus Improve both effectiveness and efficiency

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Classification of Constraints We have the following classification of

constraints Anti-monotone Monotone Succinct Convertible

Convertible anti-monotone Convertible monotone Strongly convertible

Inconvertible

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Anti-Monotone Definition 1 (Anti-Monotone): A 1-var

constraint C is anti-monotone if for all sets S, S’: S S’ & S satisfies C S’ satisfies C.

Simply, when an intemset S violates

the constraint, so does any of its

superset

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Is Min(S) v anti-monotone?

S={5, 10, 14}, v = 7

Min(S) 7

{5} violates it. Superset {5}: {5, 10}, {5, 14}, {5, 10 ,

14}So does {5, 10}, {5, 14}, {5, 10 , 14}

Min(S) v is anti-monotone

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Succinct Definition 2 (Succinct)

I Item is a succinct set if it can be expressed as p(Item) for some selection predicate p.

SP 2Item is a succinct powerset if there is a fixed number of succinct sets Item1, … Itemk Item such that SP can be expressed in terms of the strict powersets of Item1,…,Itemk, using union and minus.

Finally, a 1-var constraint C is succinct provided SATc(Item) is a succinct powerset.

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Succinct General idea: we can enumerate

all and only those sets that are guaranteed to satisfy the constraint.

If a constraint is succinct, we can directly generate precisely the sets that satisfy it.

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Succinct example

Itemset containing a or b

Itemset containing some item with

value more than 30

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Succinct example C1 Item.Price 100

Item 1 = Item.price 100(Item)={a,b} 2Item1={{a}, {b}, {a, b}} SATc1 = {{a}, {b}, {a, b}} SATc1 = 2Item1

C1 is succinct

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Convertible Convert tough constraints into

anti-monotone or monotone by properly order items

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Convertible Definition: R is an order of items Convertible anti-monotone

Itemset X satisfies constraint so does every prefix of X w.r.t. R

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Convertible example constraint C: avg(X) 25

Order items in value-descending order

<a, f, g, d, b, h, c, e>

Itemset afd satisfies C So do prefixes a and af Thus, it becomes

Anti-monotone!

Item Value

a 40b 0c -20d 10e -30f 30g 20h -10

Item Value

a 40f 30g 20d 10b 0h -10c -20e -30

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Commonly Used Constraints— A General Picture

Constraint Antimonotone Monotone Succinct

v S no yes yes

S V no yes yes

S V yes no yes

min(S) v no yes yes

min(S) v yes no yes

max(S) v yes no yes

max(S) v no yes yes

count(S) v yes no weakly

count(S) v no yes weakly

sum(S) v ( a S, a 0 )

yes no no

sum(S) v ( a S, a 0 )

no yes no

range(S) v yes no no

range(S) v no yes no

avg(S) v, { , , }

convertible convertible no

support(S) yes no no

support(S) no yes no

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Optional Proof of min(S) v is Anti-monotone According to the table, min(S) v

is both anti-monotone and succinct.

I only proof anti-monotone here due to time limitation.

Something special…

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Constraint Classification

Convertibleanti-monotone

Convertiblemonotone

Stronglyconvertible

Inconvertible

Succinct

Antimonotone

Monotone

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Summary of ApproachRecapitulation

Basic idea about mining frequent itemsets with constraints.

Introduce several important constraints.

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Algorithms There are many algorithms in

solving constrained based association rules mining. Algorithm Direct Algorithm MultiJoins & Reorder Algorithm Apriori† Algorithm Hybrid(m) Algorithm CAP (Main Focus)

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Design of Algorithm Sound

An algorithm is sound provided it only finds frequent sets that satisfy the given constraints.

Complete An algorithm is complete provided all

frequent sets satisfying the given constraints are found.

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Algorithm Apriori†

Main idea : Use Apriori Algorithm to get the frequent item sets. Then apply the constraints on the item sets found.

Step 1) Apriori with Cfreq

Step 2) Apply C – Cfreq to get final Ans

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Algorithm Apriori†

(Pseudocode)1. C1 consists of sets of size 1; k = 1; Ans = ;

2. While (Ck not empty) {

2.1 conduct db scan to form Lk from Ck;

2.2 form Ck+1 from Lk based on Cfreq; k++; }

3. For each set S in some Lk:

Add S to Ans if S satisfies (C – Cfreq).

The Apriori† Algorithm — An Example

Database TDB

1st scan

C1L1

L2

C2 C2

2nd scan

C3 L33rd scan

Tid Items

10 A, C, D

20 B, C, E

30 A, B, C, E

40 B, E

Itemset

sup

{A} 2

{B} 3

{C} 3

{D} 1

{E} 3

Itemset

sup

{A} 2

{B} 3

{C} 3

{E} 3

Itemset

{A, B}

{A, C}

{A, E}

{B, C}

{B, E}

{C, E}

Itemset

sup

{A, B} 1{A, C} 2{A, E} 1{B, C} 2{B, E} 3{C, E} 2

Itemset

sup

{A, C} 2{B, C} 2{B, E} 3{C, E} 2

Itemset

{B, C, E}

Itemset

sup

{B, C, E}

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The Apriori† Algorithm — An Example (cont.)

Database TDB

L2

Tid Items

10 A, C, D

20 B, C, E

30 A, B, C, E

40 B, E

Itemset

sup

{A} 2

{B} 3

{C} 3

{E} 3

Itemset

sup

{A, C} 2{B, C} 2{B, E} 3{C, E} 2

Itemset

sup

{B, C, E}

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L3

L1 Constraint : {A, C, E}

T.ItemAns

{A}{C}{E}

{A, C}{C, E}

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Algorithm CAP Succinct and Anti-monotone

Strategy I: Replace C1 in the Apriori Algorithm by C1

C.

Anti-monotone but non-succinct Strategy II: Define Ck as in the Apriori

Algorithm. Drop a set S Ck from counting if S fails C, i.e., constraint satisfaction is tested before counting is done.

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Algorithm CAP (cont.) Succinct but non-anti-monotone

Strategy III: Too Complicated. To be discussed later…

Non-succinct & non-anti-monotone Strategy IV: Induce any weaker constraint C1

from C. Depending on whether C1 is anti-monotone and/or succinct, use one of the strategies I-III above for the generation of frequent set.

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Algorithm CAP (Pseudocode)1 if Csam Csuc Cnone is non-empty, prepare C1 as indicated in

Strategies I, III, and IV; k = 1;2 if Csuc is non-empty {

2.1 conduct db scan to form L1 as indicated in Strategy III;

2.2 form C2 as indicated in Strategy III; k = 2;}

3 while (Ck not empty) {

3.1 conduct db scan to form Lk from Ck;

3.2 form Ck+1 from Lk based on Strategy III if Csuc is non-empty, and Strategy II for constraints in Cam;}

4. if Cnone is empty, Ans = ULk. Otherwise, for each set S in some Lk, add S to Ans iff S satisfies Cnone.

The Algorithm CAP — An Example

Database TDB

Tid Items

10 A, C, D

20 B, C, E

30 A, B, C, E

40 B, E

Constraints : {A, C, E} T.Item & min support count = 2 Question : Which strategy should we apply?

The Algorithm CAP — An Example (Cont.)

Database TDB

1st scanC1

L1

L2

C2

C2

2nd scan

C3

Tid Items

10 A, C, D

20 B, C, E

30 A, B, C, E

40 B, E

Itemset

sup

{A} 2

{C} 3

{E} 3

Itemset

sup

{A} 2

{C} 3

{E} 3

Itemset

{A, C}

{A, E}

{C, E}

Itemset

sup

{A, C} 2{A, E} 1{C, E} 2

Itemset

sup

{A, C} 2{C, E} 2

Itemset

{}

Because {A, E} is pruned earlier

Ans

{A}{C}{E}

{A, C}{C, E}

Apply Strategy I!!!

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Case 3 : Succinct but not anti-monotone. Revisit…

{1} {2} {3} {4} {1,2} {2,3}………{3,4}

………{1,2,3,4}

Some possible frequent sets may be lost: e.g. {1,8} {1,2,10}

Apriori

{1} {2} {3} {4} {5} {6} {7} {8} {9} {10} min (S) < 5

{1} {2} {3} {4}

**Information extracted from past presentation.

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Case 3 : Succinct but not anti-monotone. Continue…

Algorithm Direct Idea : Play it safe. Generate Cc

k+1 by using Lc

k x F where F is the set of all frequent items.

Algorithm MultiJoins Algorithm Reorder

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Performance Analysis (Specification) Programs written in C Generate transactional databases

using program from IBM Almaden Research Center

100,000 records, domain of 1,000 items

Page size 4KB SPARC-10 environment

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Performance Analysis (Terminology) Speedup

Comparison of execution time between two algorithms.

Item Selectivity x% of them items satisfying the constraints.

Support Threshold *Low support threshold means more

frequent set to process.

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Performance Analysis Note: Support

threshold set at 0.5%.

For 10% selectivity, CAP runs 80 times faster than Apriori†!

For 30% selectivity, the speedup is about 10 times.

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Performance Analysis Note: Item Selectivity

fixed at 30%.

Support threshold goes up, frequent item set goes down, Apriori† improves.

CAP still at least 8 times faster.

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Performance Analysis

Each entry is of the form a/b a is the # of frequent set satisfying the constraint. B is the total number of frequent set.

For L4 with support of 0.2%, Apriori† finds 1250 frequent sets where 8 of which is found by CAP.

Support L1 L2 L3 L4 L5 L6 L7 L8

0.2% 174/582 79/969 29/1140 8/1250 1/934 0/451 0/132 0/20

0.6% 98/313 1/12 0/1 0 0 0 0 0

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Conclusion The idea of anti-monotonicity,

succinctness, and convertible are introduced in the paper.

Sound, complete, and efficient algorithms are introduced for the constraint based association rule mining.

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Reference R. Srikant, Q. Vu, and R. Agrawal. Mining

association rules with item constraints. KDD’97.

R. Ng, L. V. S. Lakshmanan, J. Han, and A. Pang. Exploratory mining and pruning optimizations of constrained associations rules. SIGMOD’98.

J. Pei and J. Han. Can we push more constraints into frequent pattern mining? KDD’00.

1 mining association rules with constraints wei ning joon wong cosc 6412 presentation

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