FS-Miner : Efficient and Incremental Mining of Frequent Sequence Patterns in Web L ogs

FS-Miner : Efficient and FS-Miner : Efficient and Incremental Mining of Incremental Mining of

Frequent Sequence Patterns Frequent Sequence Patterns in Web Logsin Web LogsMaged EL-Sayed, Carolina Ruiz, and Elke A. Maged EL-Sayed, Carolina Ruiz, and Elke A.

RundensteinerRundensteiner

6th ACM International Workshop on Web Information and 6th ACM International Workshop on Web Information and Data Management (WIDM 2004), pp.128-135, 2004Data Management (WIDM 2004), pp.128-135, 2004

November 12-13, 2004, Washington, DC, USANovember 12-13, 2004, Washington, DC, USA

Advisor: Professor Hsin-Hsi ChenAdvisor: Professor Hsin-Hsi ChenReporter: Clarence Min-Chi HsiehReporter: Clarence Min-Chi Hsieh

Natural Language Processing Laboratory,Natural Language Processing Laboratory,Dept. of Computer Science and Info. Dept. of Computer Science and Info.

Engineering, NTUEngineering, NTU2005/10/112005/10/11

SlideSlide - - 22Copyright © Natural Language Processing Lab., NTU, 2005Copyright © Natural Language Processing Lab., NTU, 2005

Reporter: Clarence Min-Chi HsiehReporter: Clarence Min-Chi Hsieh FS-Miner : Efficient and Incremental MiningFS-Miner : Efficient and Incremental Mining of Frequent Sequence Patterns in Web Logsof Frequent Sequence Patterns in Web Logs

OutlineOutlineIntroductionIntroductionFS-Tree ConstructionFS-Tree ConstructionMining the FS-TreeMining the FS-TreeMaintaining the FS-Tree Maintaining the FS-Tree

IncrementallyIncrementallyMining the FS-Tree IncrementallyMining the FS-Tree IncrementallyInteractive MiningInteractive MiningExperimental EvaluationExperimental EvaluationConclusionsConclusions



IntroductionIntroduction

Path Traversal PatternPath Traversal Pattern– FS, SSFS, SS– AABBC, BC, BCCD…D…

Web Traversal PatternWeb Traversal Pattern– IPA, MFTPIPA, MFTP– AABBDDCCA, CA, CAACCAADDB…B…



Introduction Introduction (Cont.)(Cont.)

Consider Backward TraversalConsider Backward TraversalSubsequenceSubsequence

– Need Need ContinuousContinuousMSuppRMSuppRlinklink System Define System DefineMSuppRMSuppRseqseq User Define User DefineMSuppCMSuppClinklink

MSuppCMSuppCseqseq



FS-Tree ConstructionFS-Tree Construction

SIDSID InSeqInSeq11 dgidgi22 dgdg33 cdehicdehi44 cdecde55 cbcdgcbcdg66 cbcb77 abcdgiabcdgi88 abcdabcd99 bdehibdehi

1010 bdehbdeh1111 cdebfabccdebfabc1212 cdefabccdefabc1313 aicaic1414 diedie1515 igdbaigdba1616 efaefa1717 efef1818 efabefab

SIDSID InSeqInSeq

MSuppCMSuppClinklink=2=2

MSuppCMSuppCseqseq=3=3

Total # of links = 50Total # of links = 50

MSuppRMSuppRlinklink=4%=4%

MSuppRMSuppRseqseq=6%=6%

System Define:System Define: MSuppR MSuppRlinklink

User Define:User Define: MSuppR MSuppRseqseq



FS-Tree Construction FS-Tree Construction (Cont.)(Cont.)

LinkLinkCountCountd-gd-g 44g-ig-i 22c-dc-d 77d-ed-e 66e-he-h 33h-ih-i 22c-bc-b 22b-cb-c 55

f-af-a 22

a-ba-b 44b-db-d 22e-be-b 11

LinkLinkCountCount

b-fb-fe-fe-fa-ia-ii-ci-cd-id-ii-ei-ei-gi-gg-dg-dd-bd-bb-ab-a

11111111111111111111

SIDSID InSeqInSeq11 dgidgi22 dgdg33 cdehicdehi44 cdecde55 cbcdgcbcdg66 cbcb77 abcdgiabcdgi88 abcdabcd99 bdehibdehi

1010 bdehbdeh1111 cdebfabccdebfabc1212 cdefabccdefabc1313 aicaic1414 diedie1515 igdbaigdba1616 efaefa1717 efef1818 efabefab

SIDSID InSeqInSeq




LinkLink CountCount

d-gd-g 44g-ig-i 22c-dc-d 77d-ed-e 66e-he-h 33h-ih-i 22c-bc-b 22b-cb-c 55

f-af-a 22

a-ba-b 44b-db-d 22e-be-b 11

LinkLink CountCount


11111111111111111111

LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22

ListHListHHeader Table (HT)Header Table (HT)

e-be-b 11LinkLink CountCount


11111111111111111111

1111SIDSID

1111121213131313141414141515151515151515

Non-Frequent Non-Frequent Links Table(NFLT)Links Table(NFLT)

When FS-Tree BuiltWhen FS-Tree Built




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq11 dgidgi

dd

gg

i:1i:1

11

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq22 dgdg

dd

g:2g:2

i:1i:1

22

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq33 cdehicdehi

dd

g:2g:2

i:1i:1

22

11

cc

dd

ee

hh

i:3i:3

11

11

11

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq44 cdecde

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

22

22

11

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq55 cbcdgcbcdg

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

22

22

11

11

bb

cc

dd

g:5g:5

11

11

11

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq66 cbcb

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

22

22

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq77 abcdgiabcdgi

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

22

22

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

dd

gg

i:7i:7

11

11

11

11

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq88 abcdabcd

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

22

22

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq99 bdehibdehi

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

22

22

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

hh

i:9i:9

11

11

11

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq1010 bdehbdeh

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

22

22

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq1111 cdcdebfebfabcabc

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

33

33

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

11

11

11




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq1212 cdcdefefabcabc

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

44

44

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

22

22

22




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq1313 aicaic

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

44

44

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

22

22

22




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq1414 diedie

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

44

44

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

22

22

22




LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRootSIDSID InSeqInSeq1515 gdbagdba

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

44

44

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

22

22

22



Mining the FS-TreeMining the FS-Tree

Step 1: Extracting Derived PathsStep 1: Extracting Derived PathsStep 2: Constructing Conditional Step 2: Constructing Conditional

Sequence BaseSequence BaseStep 3: Constructing Conditional Step 3: Constructing Conditional

FS-TreeFS-TreeStep 4: Extracting Frequent Step 4: Extracting Frequent

SequencesSequences



Mining the FS-Tree Mining the FS-Tree (Cont.)(Cont.)

Step 1Step 1LinkLink CountCount


f-af-a 22

a-ba-b 44b-db-d 22


RootRoot

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

44

44

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

22

22

22




Step 2Step 2RootRoot

cc

dd

e:4e:4

hh

44

44

11

bb

dd

ee

h:10h:10

22

22

22

Conditional Sequence base :Conditional Sequence base :

Step 3Step 3 Conditional FS-Tree:Conditional FS-Tree:

(c-d:1, d-e:1), (b-d:2, d-e:2)(c-d:1, d-e:1), (b-d:2, d-e:2)

RootRoot

ee

dd

cc bb

33

11 22

RootRoot

ee

dd

11

RootRoot

ee

dd

cc

11

11

RootRoot

ee

dd

cc

33

11




Step 4Step 4

Depth first traversalDepth first traversal

RootRoot

ee

dd

cc bb

33

11 22<<deh deh : 3>: 3>

OutputOutput




The AnswersThe AnswersLinkLink d-gd-g

Derived PathsDerived Paths(d-g:2)(d-g:2)

(c-b:2, b-c:1, c-d:1, d-g:1)(c-b:2, b-c:1, c-d:1, d-g:1)(a-b:2, b-c:2, c-d:2, d-g:1)(a-b:2, b-c:2, c-d:2, d-g:1)

Conditional Sequence basesConditional Sequence bases

(c-b:1, b-c:1, c-d:1)(c-b:1, b-c:1, c-d:1)(a-b:1, b-c:1, c-d:1)(a-b:1, b-c:1, c-d:1)Conditional FS-TreesConditional FS-Trees

Frequent SequencesFrequent Sequences

LinkLink c-dc-dDerived PathsDerived Paths

(c-d:4)(c-d:4)(c-b:2, b-c:1, c-d:1)(c-b:2, b-c:1, c-d:1)(a-b:2, b-c:2, c-d:2)(a-b:2, b-c:2, c-d:2)Conditional Sequence basesConditional Sequence bases

(c-b:1, b-c:1)(c-b:1, b-c:1)(a-b:2, b-c:2)(a-b:2, b-c:2)

Conditional FS-TreesConditional FS-Trees

(b-c:3)(b-c:3)Frequent SequencesFrequent Sequences

<bcd <bcd : 3>: 3>




The AnswersThe Answers

LinkLink e-he-hDerived PathsDerived Paths

(c-d:4, d-e:4, e-h:1)(c-d:4, d-e:4, e-h:1)(b-d:3, d-e:2, e-h:2)(b-d:3, d-e:2, e-h:2)Conditional Sequence basesConditional Sequence bases

(c-d:1, d-e:1)(c-d:1, d-e:1)(b-d:2, d-e:2)(b-d:2, d-e:2)


(d-e:3)(d-e:3)Frequent SequencesFrequent Sequences

<<deh deh : 3>: 3>

LinkLink d-ed-eDerived PathsDerived Paths(c-d:4, d-e:4)(c-d:4, d-e:4)(b-d:3, d-e:2)(b-d:3, d-e:2)


(c-d:4)(c-d:4)(b-d:2)(b-d:2)


(c-d:4)(c-d:4)Frequent SequencesFrequent Sequences

<<cde cde : 4>: 4>




The AnswersThe Answers

LinkLink a-ba-bDerived PathsDerived Paths

(a-b:2)(a-b:2)(f-a:2, a-b:2)(f-a:2, a-b:2)


(f-a:2)(f-a:2)Conditional FS-TreesConditional FS-Trees


LinkLink b-cb-cDerived PathsDerived Paths(c-b:2, b-c:1)(c-b:2, b-c:1)(a-b:2, b-c:2)(a-b:2, b-c:2)

(f-a:2, a-b:2, b-c:2)(f-a:2, a-b:2, b-c:2)Conditional Sequence basesConditional Sequence bases

(c-b:1)(c-b:1)(a-b:2)(a-b:2)

(f-a:2, a-b:2)(f-a:2, a-b:2)Conditional FS-TreesConditional FS-Trees

(a-b:4)(a-b:4)Frequent SequencesFrequent Sequences

<abc : 4><abc : 4>



Maintaining the FS-Tree Maintaining the FS-Tree IncrementallyIncrementally

1616 efaefa1717 efef1818 efabefab

SIDSID InSeqInSeqe-f:3e-f:3f-a:2f-a:2a-b:1a-b:1

MSuppCMSuppClinklink=2=2

MSuppCMSuppCseqseq=3=3

e-f in NFLT Becomes e-f in NFLT Becomes Frequent, Move to Frequent, Move to Table HT Table HT

LinkLink CountCount

e-fe-f 11SIDSID1212

Non-Frequent Non-Frequent Links Table(NFLT)Links Table(NFLT)

1212 cdefabccdefabcSIDSID InSeqInSeq

Retrieve the Sequence Retrieve the Sequence from Original DBfrom Original DBDelete this record from NFLTDelete this record from NFLT

(Move to HT)(Move to HT)



Maintaining the FS-Tree IncrementallyMaintaining the FS-Tree Incrementally (Cont.)(Cont.)

LinkLink CountCount


f-af-a 44

a-ba-b 55b-db-d 22


RootRootSIDSID InSeqInSeq1212 cdcdefefabcabc

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

44

44

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

11

11

11

e-fe-f 44

ff

aa

bb

c:12c:12

11

11

11

11

DeleteDelete




LinkLink CountCount


f-af-a 44

a-ba-b 55b-db-d 22


RootRootSIDSID InSeqInSeq1616 efaefa

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

44

44

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

11

11

11

e-fe-f 44

ff

aa

bb

c:12c:12

11

11

11

11

ee11

ff

a:16a:1611




LinkLink CountCount


f-af-a 44

a-ba-b 55b-db-d 22


RootRootSIDSID InSeqInSeq1717 efef

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

44

44

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

11

11

11

e-fe-f 44

ff

aa

bb

c:12c:12

11

11

11

11

ee22

f:17f:17

a:16a:1611




LinkLink CountCount


f-af-a 44

a-ba-b 55b-db-d 22


RootRootSIDSID InSeqInSeq1818 efabefab

dd

g:2g:2

i:1i:1

22

11

cc

dd

e:4e:4

hh

i:3i:3

44

44

11

11

b:6b:6

cc

dd

g:5g:5

22

11

11

11

aa

cc

bb

d:8d:8

gg

i:7i:7

22

22

22

11

11

bb

dd

ee

h:10h:10

i:9i:9

22

22

22

11

ff

aa

bb

cc

11

11

11

e-fe-f 44

ff

aa

bb

c:12c:12

11

11

11

11

ee33

f:17f:17

a:16a:1622

b:18b:1811



Mining the FS-Tree IncrementallyMining the FS-Tree Incrementally Type 1:Type 1:

– Mine for those Links if they are AffectedMine for those Links if they are Affected Type 2 and 4:Type 2 and 4:

– Mine for these LinksMine for these Links Type 3 and 5:Type 3 and 5:

– Delete Previously Discovered Patterns that Include these Delete Previously Discovered Patterns that Include these LinksLinks

Type 6, 7, 8, and 9:Type 6, 7, 8, and 9:– Do NothingDo Nothing

FrequentFrequentLinksLinks

PotentiallyPotentiallyFrequentFrequent

LinksLinks

Non-FrequentNon-FrequentLinksLinks

Header Table (HT)Header Table (HT)Non-Frequent Non-Frequent

Links Table (NFLT)Links Table (NFLT)11

2233 44

55

66

7788

99



Mining the FS-Tree IncrementallyMining the FS-Tree Incrementally (Cont.)(Cont.)

The AnswersThe Answers LinkLink a-ba-bDerived PathsDerived Paths

(c-d:4, d-e:4, e-f:1, f-a:1, a-b:1)(c-d:4, d-e:4, e-f:1, f-a:1, a-b:1)(a-b:2)(a-b:2)

(f-a:1, a-b:1)(f-a:1, a-b:1)(e-f:3, f-a:2, a-b:1)(e-f:3, f-a:2, a-b:1)Conditional Sequence basesConditional Sequence bases

(c-d:1, d-e:1, e-f:1, f-a:1)(c-d:1, d-e:1, e-f:1, f-a:1)(f-a:1)(f-a:1)

(e-f:1, f-a:1)(e-f:1, f-a:1)Conditional FS-TreesConditional FS-Trees

(f-a:3)(f-a:3)Frequent SequencesFrequent Sequences

<fab <fab : 3>: 3>

LinkLink CountCount ListHListHHeader Table (HT)Header Table (HT)


f-af-a 44

a-ba-b 55b-db-d 22

e-fe-f 44



Mining the FS-Tree IncrementallyMining the FS-Tree Incrementally (Cont.)(Cont.)

The AnswersThe AnswersLinkLink e-fe-f

Derived PathsDerived Paths(c-d:4, d-e:4, e-f:1)(c-d:4, d-e:4, e-f:1)

(e-f:3)(e-f:3)Conditional Sequence basesConditional Sequence bases

(c-d:1, d-e:1)(c-d:1, d-e:1)



LinkLink f-af-aDerived PathsDerived Paths

(c-d:4, d-e:4, e-f:1, f-a:1)(c-d:4, d-e:4, e-f:1, f-a:1)(f-a:1)(f-a:1)

(e-f:3, f-a:2)(e-f:3, f-a:2)Conditional Sequence basesConditional Sequence bases

(c-d:1, d-e:1, e-f:1)(c-d:1, d-e:1, e-f:1)(e-f:2)(e-f:2)


(e-f:3)(e-f:3)Frequent SequencesFrequent Sequences

<efa <efa : 3>: 3>



Interactive MiningInteractive Mining

Setting the Setting the MSuppCMSuppClinklink to a to a Small Enough ValueSmall Enough Value– Enough Information in the Enough Information in the FS-FS-

TreeTree– Without to Reference the Without to Reference the

Original DatabaseOriginal Database



Experimental EvaluationExperimental Evaluation

MS Data SetMS Data Set– Microsoft Anonymous Web Data SetMicrosoft Anonymous Web Data Set– 32,711 Sessions32,711 Sessions

1 up to 35 page references1 up to 35 page references

– 294 distinct pages294 distinct pages MSNBC Data SetMSNBC Data Set

– MSNBCMSNBC Anonymous Web Data SetAnonymous Web Data Set– 989,818 Sections989,818 Sections

1 up to several thousands of page reference1 up to several thousands of page reference

– 17 distinct pages17 distinct pages http://kdd.ics.uci.eduhttp://kdd.ics.uci.edu



Experimental Evaluation Experimental Evaluation (Cont.)(Cont.)

Scalability with the Number of Input SessionsScalability with the Number of Input Sessions– MS Data SetMS Data Set

No No MSuppRMSuppRseqseq????




Scalability with the Number of Input SessionsScalability with the Number of Input Sessions– MSNBC Data SetMSNBC Data Set

No No MSuppRMSuppRseqseq????




Scalability with Support ThresholdScalability with Support Threshold– MS Data SetMS Data Set




Scalability with Support ThresholdScalability with Support Threshold– MSNBC Data SetMSNBC Data Set




Incremental MiningIncremental Mining– MS Data SetMS Data Set




Incremental MiningIncremental Mining– MSNBC Data SetMSNBC Data Set



ConclusionsConclusionsTwo Scans for the Input DatabaseTwo Scans for the Input DatabaseAllows for Incremental Discovery Allows for Incremental Discovery

of Frequent Sequences when the of Frequent Sequences when the Input Database is UpdatedInput Database is Updated

Allows Interactive Response to Allows Interactive Response to Changes to the Minimun SupportChanges to the Minimun Support

FS-Miner : Efficient and Incremental Mining of Frequent Sequence Patterns in Web L ogs

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Transcript of FS-Miner : Efficient and Incremental Mining of Frequent Sequence Patterns in Web L ogs