Kha Lun Mn DataMiningNghin Cu Phn Loi Vn Bn Ting Vit CHNG 1 :
TNG QUAN Ngy ny , s bng n thng tin do b tc ng bi s xut hin ca cc
siu phng tin v World Wide Web (WWW) lm cho khng gian d liu gia tng
thng xuyn , iu ny to ra mt thch thc cho cc h thng truy vn thng tin
sao cho c hiu qa . Mt trong nhng kh khn m cc h thng thng tin thng
phi gp l tn sut cp nht ca cc thng tin qa ln .Phng thc s dng giy
trong giao dch ang dn c s ha , do nhiu tnh nng vt tri m phng thc ny
mang li , nh l c th lu tr lu di , cp nht , sa i , tm kim mt cch
nhanh chng . Do s lng vn bn s ha ngy nay ang tng dn theo cp s nhn ,
cng vi s gia tng ca s lng vn bn , nhu cu tm kim vn bn cng tng theo
, khi phn loi vn bn t ng l mt yu cu cp thit c t ra . Phn loi vn bn
gip s gip chng ta tm kim thng tin mt cch nhanh chng hn thay v phi
tm ln lt trong tng vn bn , hn na khi m s lng vn bn ang gia tng mt
cch nhanh chng th thao tc tm ln lt trong tng vn bn s mt rt nhiu thi
gian , cng sc v l mt cng vic nhm chn v khng kh thi. Chnh v th nhu
cu phn loi vn bn t ng l thc s cn thit.Hin nay c rt nhiu cng trnh
nghin cu v phn loi vn bn v c c nhng kt qa ng khch l, nh l : Support
Vector Machine , K Nearest Neighbor , Linear Least Squares Fit ,
Neural Network , Nave Bayes , Centroid Based im chung ca cc phng
php ny u da vo xc sut thng k hoc da vo trng s ca cc t , cm t trong
vn bn .Trong mi phng phpu c cch tnh ton khc nhau , tuy nhin cc phng
php ny u phi thc hin mt s bc chung , nh: u tin mi phng php s da vo
thng tin v s xut hin ca cc t trong vn bn ( tn s xut hin trong tp vn
bn ,) biu din thnh dng vector , sau ty tng bi ton c thm chng ta s
quyt nh chn p dng phng php no , cng thc tnh ton no cho ph hp phn
loi tp vn bn da trn tp cc vector xy dng c bc trn , nhm mc ch t c kt
qa phn loi tt nht .CHNG 2 : CC HNG TIP CN PHN LOI VN
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vin : Trnh Quc Sn-CH04010471Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit Cng vi cc hng nghin cu khc v x l v rt trch thng tin
trong vn bn nh phn cm ( clustering) , tng luc vn bn ( text
summarization ) , phn loi vn bn t ng l mt hng nghin cu c quan tm
trong nhiu nm gn y . phn loi vn bn cc cng trnh nghin cu thng da vo
t kha , da trn ng ngha ca t , tp th hay mt s m hnh khc .I. Biu din
vn bn Nh trnh by phn trn , bc u tin trong qui trnh phn loi vn bn l
thao tc chuyn vn bn ang c m t dui dng chui cc t thnh mt m hnh khc ,
sao cho ph hp vi cc thut ton phn loi ,thng thng ngui ta thng biu
din vn bn bng m hnh vector. tng ca m hnh ny l xem mi mt vn bn ( Di
)c biu din theo dng( ) i ,dDii , trong i l ch s dng nhn din vn bn
ny v dil vector c trng ca vn bn Di ny , trong : ) ,....., , (w w
wdin 2 i 1 ii , v n l slungc trngca vector vnbn,wijltrngsca c
trngthj , { } n 1,2,..., j .Mt vn cn quan tm khi biu din vn bn theo
vector c trng chnh l vic chn la c trng v s chiu cho khng gian
vector . Cn phi chn bao nhiu t , l cc t no , phng php chn ra sao ?
. y l cu hi chng ta phi tr li trong qa trnh chuyn vn bn sang thnh
vector , c nhiu cch tip cn khc nhau tr li cho cu hiny,
tiubiulsdngphngphpInformationGain, phngphpDF Thresolding hay phng
php Term Strength . Phng php Information Gain s dng o MI ( Mutual
Information) chn ra tp t kha c trng c o MI cao nht . Tuy nhin , vic
chn la phng php no th tu thuc vo thch hp , ph hp ca phng php , ca o
m phng php s dng so vi bi ton m chng ta ang
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vin : Trnh Quc Sn-CH04010472Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit xem xt gii quyt , c th l nu vn bn l mt trang web th
s c phng php chn la c trng khc so vi cc vn bn loi khc .Cc c trng ca
vn bn khi biu din di dng vector :- S nhiu khng gian c trng thng ln
.- Cc c trng c lp nhau.- Cc c trng ri rc :vector c trng di c th c
nhiu thnh phn mang gi tr 0 do c nhiu c trng khng xut hin trong vn
bn di (nu chng ta tip cn theo cch s dng gi tr nh phn 1 , 0 biu din
cho vic c xut hin hay khng mt c trng no trong vn bn ang c biu din
thnh vector) , tuy nhin nu n thun cch tip cn s dng gi tr nh phn 0 ,
1 ny th kt qa phn loi phn no hn ch l do c th c trng khng c trong vn
bn ang xt nhng trong vn bn ang xt li c t kha khc vi t c trng nhng c
ng ngha ging vi t c trng ny , do mt cch tip cn khc l khng s dng s
nh phn 0 ,1 m s dng gi tr s thc phn no gim bt s ri rc trong vector
vn bn.II.Cc phng php phn loi vn bnII.1. Phng php SVM Support Vector
MachineSVM l phng php phn loi rt hiu qa c Vapnik gii thiu nm 1995 .
tng ca phng php l cho trc mt tp hun luyn c biu din trong khng gian
vector , trong mi mt vn bn c xem nh mt im trong khng gian ny .Phng
php ny tm ra mt siu mt phng h quyt nh tt nht c th chia cc im trn
khng gian ny thnh hai lp ring bit tng ng ,tm gi l lp + ( cng ) v lp
( tr) .Cht lng ca siu mt phng ny c quyt nh bi mt khong cch ( c gi l
bin) ca im d liu gn nht ca mi lp n mt phng ny . Khong cch bin cng
ln th cng c s phn chia tt cc im ra thnh hai lp , ngha l s t c kt qa
phn loi tt . Mc tiu ca thut ton SVM l tm c khong cch bin ln nht to
kt qa phn loi tt
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vin : Trnh Quc Sn-CH04010473Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit C th ni SVM thc cht l mt bi ton ti u , mc tiu ca
thut ton l tm c mt khng gian H v siu mt phng quyt nh h trn H sao
cho sai s khi phn loi l thp nht , ngha l kt qa phn loi s cho kt qa
tt nht .Phng trnh siu mt phng cha vector di trong khng gian nh sau
:0 bw.di +'< +> ++
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0 bw .di,0 b w .di,w .disigndih Nh th vector h(di) biu din s phn
lp ca vector di vo hai lp . Gi Yi mang gi tr +1 hoc -1 , khi Yi =
+1 vn bn tng ng vi vector dithuc lp + v ngc li n s thuc vo lp - .
Khi ny c siu mt phng h ta s gii bi ton sau : Tm Minwvi w v b tha iu
kin : 1 b)) wdi(sign( yi: n 1, i + Chng ta thy rng SVM l mt phng
quyt nh ch ph thuc vo cc vector h trc khong cch n mt phng quyt nh
l1/wi. Khi cc im khc b xa i th thut ton vn cho kt qa ging nh ban u
. Chnh c im ny lm cho SVM khc vi cc thut ton khc nh kNN , LLSF ,
Nnet , NB v tt c d liu trong tp hun luyn u c dng ti u ha kt qa
.II.2. Phng php K Nearest Neighbor ( kNN)kNN l phng php truyn thng
kh ni ting theo hng tip cn thng k c nghin cu trong nhiu nm qua .
kNN c nh gi l mt trong nhng phng php tt nht c s dng t nhng thi k u
trong nghin cu v phn loi vn bn
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vin : Trnh Quc Sn-CH04010474Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit tng ca phng php ny l khi cn phn loi mt vn bn mi ,
thut ton s xcnhkhongcch(cthpdngcccngthcvkhongcchnhEuclide, Cosine ,
Manhattan , ) ca tt c cc vn bn trong tp hun luyn n vn bn ny tm ra k
vn bn gn nht ,gi l k nearest neighbor k lng ging gn nht , sau dng
cc khong cch ny nh trng s cho tt c cc ch . Khi , trng s ca mt ch
chnh l tng tt c cc khong cch trn ca cc vn bn trong k lng ging c cng
ch , ch no khng xut hin trong k lng ging s c trng s bng 0 . Sau cc
ch s c sp xp theo gi tr trng s gim dn v cc ch c trng s cao s c chn
lm ch ca vn bn cn phn loi.Trng s ca ch cj i vi vn bn x c tnh nh sau
: bjcj,diy .{kNN}didi,xsim cjx,W
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Trong : y (di, c) thuc {0,1} , vi :- y = 0 : vn bn di khng thuc
v ch cj- y = 1 : vn bn di thuc v ch cjsim (x , d) : ging nhau gia
vn bn cn phn loi x v vn bn d . Chng ta c th s dng o cosine tnh
khong cch :dixdi.xdi,xcosdi,xsim
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- bj l ngng phn loi ca ch cj c t ng hc s dng mt tp vn bn hp l c
chn ra t tp hun luyn. chn c tham s k tt nht cho thao tc phn loi ,
thut ton cn c chy th nghim trn nhiu gi tr k khc nhau , gi tr k cng
ln th thut ton cng n nh v sai st cng thp
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vin : Trnh Quc Sn-CH04010475Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit II.3.Phng php Nave Bayes (NB)NB l phng php phn loi
da vo xc sut c s dng rng ri trong lnh vc my hc v nhiu lnh vc khc nh
trong cc cng c tm kim , cc b lc mail tng c bn ca cch tip cn ny l s
dng xc sut c iu kin gia t hoc cm t v ch d on xc sut ch ca mt vn bn
cn phn loi.im quan trng ca phng php ny chnh l ch gi nh rng s xut
hin ca tt c cc t trong vn bn u c lp vi nhau. Nh th NB khng tn dng c
s ph thuc ca nhiu t vo mt ch c th . Chnh gi nh lm cho vic tnh ton
NB hiu qa v nhanh chng hn cc phng php khc vi phc tp theo s m v n
khng s dng cch kt hp cc t a ra phn on ch .Mc ch chnh l lm sao tnh c
xc sut Pr(Cj, d) , xc sut vn bn dnm trong lp Cj.Theo lut Bayes , vn
bn d s c gn vo lp Cj no c xc sut Pr(Cj, d) cao nht . Cng thc tnh
Pr(Cj, d) nh sau :( )( ) ( )( ) ( )
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cc'd'1 iC'|wiPr .c'Prd'1 iCj|wiPr .CjPrargmaxCcjd'HBAYESVi : -
TF(wi, d) l s ln xut hin ca t wi trong vn bn d- |d| l s lng cc t
trong vn bn d- wi l mt t trong khng gian c trng F vi s chiu l |F|-
Pr(Cj) c tnh da trn t l phn trm ca s vn bn mi lp tng ng ( )
CC'C'CjCCjCjPr__________________________________________________________________________Hc
vin : Trnh Quc Sn-CH04010476Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit trong tp d liu hun luyn -( )( )( ) ++Fw'cj,w'TF
Fcj,wiTF 1Cj|wiPrNgoi ra cn c cc phng php NB khc c th k ra nh ML
Nave Bayes , MAP Nave Bayes , Expected Nave Bayes . Ni chung Nave
Bayes l mt cng c rt hiu qa trong mt s trng hp. Kt qa c th rt xu nu
d liu hun luyn ngho nn v cc tham s d on (nh khng gian c trng) c cht
lng km.Nhn chung y l mt thut ton phn loi tuyn tnh thch hp trong phn
loi vn bn nhiu ch . NB c u im l ci t n gin , tc thc hin thut ton
nhanh , d dng cp nht d liu hun luyn mi v c tnh c lp cao vi tp hun
luyn .II.4. Phng php Linear Least Square Fit LLSFLLSF l mt cch tip
cn nh x c pht trin bi Yang v Chute vo nm 1992 . Ban u LLSF c th
nghim trong lnh vc xc nh t ng ngha sau s dng trong phn loi vo nm
1994 . Cc th nghim cho thy hiu sut phn loi ca LLSF c th ngang bng
vi phng php kNN kinh in. tng ca LLSF l s dng phng php hi quy hc t
tp hun luyn v cc ch c sn. Tp hun luyn c biu din di dng mt cp vector
u vo v u ra nh sau:-Vector u vo l mt vn bn bao gm cc t v trng
s.-Vector u ra gm cc ch cng vi trng s nh phn ca vn bn ng vi vector
u vo .Gii phng trnh cc cp vector u vo , u ra chng ta s thu c ma trn
ng hin ca h s hi quy ca t v ch .Phng php ny s dng cng thc :
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vin : Trnh Quc Sn-CH04010477Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit B FA2min argFFLS Trong :- A, B l ma trn i din tp d
liu hun luyn ( cc ct trong ma trn tng ng l cc vector u vo v u ra).-
FLS l ma trn kt qa ch ra mt nh x t mt vn bn bt k vo vector ca ch gn
trng s.Nh vo vic sp xp trng s ca cc ch , chng ta c mt danh sch ch c
th gn cho vn bn cn phn loi . Nh t ngng ln trng s ca cc ch m ta tm c
ch thch hp cho vn bn u vo . H thng t ng hc cc ngng ti u cho tng ch
, ging vi kNN . Mc d LLSF v kNN khc nhau v mt thng k , nhng chng ta
vn tm thy im chung trong cch lm ca hai phng php ny l qa trnh hc
ngng ti u.5. Phng php Centroid based vectorL mt phng php phn loi n
gin , d ci t v tc nhanh do c phc tp tuyn tnh O(n). tng ca cch tip
cn ny l mi lp trong d liu hun luyn s c biu din bng mt vector trng
tm . Vic xc nh lp ca mt vn bn bt k s thng qua vic tm vector trng tm
no gn vi vector biu din vn bn th nht.Lp ca vn bn chnh l lp m vector
trng tm i din v khong cch c xc nh theo o cosine.Chng ta c cng thc
tnh vector trng tm ca lp i :{i}djdj {i}1Ci o khong ccg gia vector x
v vector Ci
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vin : Trnh Quc Sn-CH04010478Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit Ci.xCi.xCi,xcos
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Trong :- x l vector vn bn cn phn loi- {i} l tp hp cc vn bn thuc
ch Ci- Ch ca vector x l Cx tha mn cos(x, Cx)= arg max
(cos(x,Ci)).III.Kt lun :Cc thut ton phn loi trn t thut ton phn loi
hai lp (SVM) n cc thut ton phn loi a lp (kNN) u c im chung l yu cu
vn bn phi c biu din di dng vector c trng . Ngoi ra cc thut ton nh
kNN , NB , LLSF u phi s dng cc c lng tham s v ngng ti u khi phn loi
vn bn , trong khi thut ton SVM c th t xc nh cc tham s ti u ny trong
qa trnh thc hin thut ton .Xt v mt thi gian , cc phng php c thi gian
hun luyn khc nhau, cc phng php kNN , NB , LLSF c thi gian hun luyn
v phn loi vn bn nhanh hn so vi cc thut ton cn li , ng thi d dng ci
t hn.Mt cu hi c t ra l : c c mt kt qa phn loi t kt qa tt th cn nhng
yu t g ? C 3 yu t quan trng tc ng n kt qa phn loi vn bn :1) Cn mt
tp d liu hun luyn chun v ln cho thut ton hc phn loi . Nu chng ta c
c mt tp d liu chun v ln th qa trnh hun luyn s tt v khi chng ta s c
kt qa phn loi tt sau khi c hc .2) Cc phng php trn hu ht u s dng m
hnh vector biu din vn bn , do phng php tch t trong vn bn ng vai tr
quan trng qa trnh biu din vn bn bng vector . Yu t ny rt quan trng ,
v c th i vi mt s ngn ng nh ting Anh chng hn th thao tc tch t trong
vn bn n gin ch l da vo cc khong trng , tuy nhin trong cc ngn ng
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vin : Trnh Quc Sn-CH04010479Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit a m tit nh ting Vit v mt s ngn ng khc th s dng khong
trng khi tch t l khng chnh xc , do phng php tch t l mt yu t quan
trng.3) Thut ton s dng phn loi phi c thi gian x l hp l , thi gian
ny bao gm : thi gian hc , thi gian phn loi vn bn , ngoi ra thut ton
ny phi c tnh tng cng (incremental function) ngha l khng phn loi li
ton b tp vn bn khi thm mt s vn bn mi vo tp d liu m ch phn loi cc vn
bn mi m thi , khi thut ton phi c kh nng gim nhiu ( noise ) khi phn
loi vn bn.CHNG 3 : CC HNG TIP CN TCH TI.CC HNG TIP CN DA TRN T :
Hng tip cn da trn t vi mc tiu tch c cc t hon chnh trong cu. Hng tip
cn ny c th chia ra theo 3 hng : da trn thng k (statistics - based)
, da trn
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vin : Trnh Quc Sn-CH040104710Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit t in ( dictionary based) v hydrid ( kt hp nhiu phng
php vi hy vng t c nhng u im ca cc phng php ny) . Hng tip cn da trn
thng k:Da trn cc thng tin nh tn s xut hin ca t trong tp hun luyn
ban u . Hng tip cn ny c bit da trn tp ng liu hun luyn , nh vy nn
hng tip cn ny t ra linh hot v hu dng trong nhiu lnh vc khc nhau.Hng
tip cn da trn t in : tng ca hng tip cn ny l nhng cm t c tch ra t vn
bn phi c so khp vi cc t trong t in. Do
tronghngtipcnnyihitinringchotnglnhvcquantm. Hng tip cn full word /
phrase cn s dng mt t in hon chnh c th tch c y cc t hoc ng trong vn
bn , trong khi hng tip cn thnh phn component li s dng t in thnh phn
.T in thnh phn ch cha cc thnh phn ca t v ng nh hnh v v cc t n gin .
Hng tip cn theo t in vn cn mt s hn ch trong vic tch t v thc hin hon
ton da vo t in . Nu nh thc hin thao tc tch t bng cch s dng t in hon
chnh th trong thc t vic xy dng mt b t in hon chnh l kh thc hin v i
hi nhiu thi gian v cng sc . Nu tip cn theo hng s dng t in thnh phn
th s gim nh hn ch , kh khn khi xy dng t in , v khi chng ta s s dng
cc hnh v t v cc t n gin v cc t khc hnh thnh nn t , cm t hon chnh.
Hng tip cn theo Hybrid : Vi mc ch kt hp cc hng tip cn khc nhau tha
hng c cc u im ca nhiu k thut v cc hng tip cn khcnhau nhm nng cao
ktqa. Hng tipcn ny thngkt hp gia hng da trn thng k v da trn t in
nhm tn dng cc mt mnh ca cc phng php ny . Tuy nhin hng tip cn Hybrid
li mt nhiu thi gian x l , khng gian a v i hi nhiu chi ph.II. CC HNG
TIP CN DA TRN K T:Trong ting vit, hnh v nh nht l ting c hnh thnh bi
nhiu k t trong bng ch ci . Hng tip cn ny n thun rt trch ra mt s lng
nht nh cc ting
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vin : Trnh Quc Sn-CH040104711Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit trong vn bn nh rt trch t 1 k t (unigram) hay nhiu k
t (n-gram) v cng mang li mt s kt qa nht nh c minh chng thng qua mt
s cng trnh nghin cu c cng b , nh ca tc gi L An H [2003] xy dng tp
ng liu th 10MB bng cch s dng phng php qui hoch ng ca i ha xc sut
xut hin ca cc ng.Ri cng trnh nghin cu ca H. Nguyn[2005] lm theo hng
tip cn l thay v s dng ng liu th , cng trnh tip cn theo hng xem
Internet nh mt kho ng liu khng l , sau tin hnh thng k v s dng thut
gii di truyn tm cch tch t ti u nht , v mt s cng trnh ca mt s tc gi
khc.Khi so snh kt qa ca tc gi L An H v H.Nguynt th thy cng trnh ca
H.Nguyn cho c kt qa tt hn khi tin hnh tch t , tuy nhin thi gian x l
lu hn.u im ni bt ca hng tip cn da trn nhiu k t l tnh n gin , d ng
dng ,ngoi ra cn c thun li l t tn chi ph cho thao tc to ch mc v x l
nhiu cu truy vn.Qua nhiu cng trnh nghin cu ca cc tc gi c cng b ,
hng tip cn tch t da trn nhiu k t ,c th l cch tch t hai k t c cho l
s la chn thch hp.III. MT S PHNG PHP TCH T TING VIT HIN
NAYIII.1.Phng php Maximum Matching : Forward / BackwardPhng php khp
ti a ( MM - Maximum Matching) hay cn gi l LRMM - Left Right Maximum
Matching. phng php ny , chng ta s duyt mt ng hoc cu t tri sang phi
v chn t c nhiu m tit nht c mt trong t in v c thc hin lp li nh vy
cho n ht cu.Dng n gin ca phng php dng gii quyt nhp nhng t n. Gi s
chng ta c mt chui k tC1, C2 , , Cn . Chng ta s p dng phng php t u
chui . u tin kim tra xem C1 c phi l t hay khng , sau kim tra xem
C1C2 c phi l t hay khng . Tip tc thc hin nh th cho n khi tm c t di
nht .Dng phc tp : Quy tc ca dng ny l phn on t .Thng thng ngi ta chn
phn on ba t c chiu di ti a. Thut ton bt u t dng n gin , c th l nu
pht hin ra nhng cch tch t gy nhp nhng, nh v d trn , gi s C1 l t v
C1C2 cng l mt t, khi chng ta kim tra k t k tip trong chui C1, C2 ,
.. ,Cn tm tt c cc on ba t c bt u vi C1 hoc C1C2
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vin : Trnh Quc Sn-CH040104712Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit V d : Gi s chng ta c c cc on sau :- C1 C2C3 C4-C1C2
C3C4C5-C1C2 C3C4 C5C6Khi chui di nht s l chui th ba . Do t u tin ca
chui th ba (C1C2)s c chn . Thc hin cc bc cho n khi c chui t honh
chnh.Nhn xt : Phng php ny thc hin tch t n gin , nhanh v ch cn da vo
t in thc hin . Tuy nhin , khuyt im ca phng php ny cng chnh l t in ,
ngha l chnh xc khi thc hin tch t ph thuc hon ton vo tnh , tnh chnh
xc ca t in.III.2.Phng php Transformation based Learning TBL :Phng
php ny tip cn da trn tp ng liu nh du .Theo cch tip cn ny cho my tnh
c th nhn bit ranh gii gia cc t c thtch t chnh xc , chng ta s cho my
hc cc cu mu trong tp ng liu c nh du ranh gii gia cc t ng .R rng
chng ta thy phng php rt n gin , v ch cn cho my hc cc tp cu mu v sau
my s t rt ra qui lut ca ngn ng v t s p dng chnh xc khi c nhng cu ng
theo lut m my rt ra . V r rng tch t c hon ton chnh xc trong mi trng
hp th i hi phi c mt tp ng liu ting Vit tht y v phi c hun luyn lu
cth rt ra cc lut y .III.3.M hnh tch t bng WFST v mng Neural :M hnh
mng chuyn dch trng thi hu hn c trng s WFST Weighted Finit State
Transducer c p dng trong tch t t nm 1996 . tng c bn l p dng WFST vi
trng s l xc sut xut hin ca mi t trong kho ng liu. Dng WFST duyt qua
cc cu cn xt , khi t c trng s ln nht l t c chn tch. Phng php ny cng
c s dng trong cng trnh c cng b ca tc gi
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vin : Trnh Quc Sn-CH040104713Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit inh in [2001] , tc gi s dng WFST km vi mng Neural kh
nhp nhng khi tch t , trong cng trnh tc gi xy dng h thng tch t gm
tng WFST tch t v x l cc vn lin quan n mt s c th ring ca ngn ng ting
Vit nh t ly , tn ring , .. v tng mng Neural dng kh nhp nhng v ng
ngha sau khi tch t (nu c).Chi tit v 2 tng ny nh sau :3.1 Tng WFST
gm c 3 bc : o Bc 1 : Xy dng t in trng s : theo m hnh WFST , thao tc
phn on t c xem nh l mt s chuyn dch trng thi c xc sut.Chng ta miu t
t in D l mt th bin i trng thi hu hn c trng s .Gi s : Hl tp cc t
chnh t ting Vit (cn gi l ting) .- P l t loi ca t . Mi cung ca D c
th l :- T mt phn t ca H ti mt phn t ca H- Cc nhn trong D biu din mt
chi ph c c lng theo cng thc : Cost =-log(f/N)Trong : f l tn s ca t
, N l kch thc tp mu.o Bc 2 : Xy dng cc kh nng phn on t : gim s bng
n t hp khi sinhrady cct ctht mtdy ccting trongcu,tcgi xut phng php
kt hp dng thm t in hn ch sinh ra cc bng n t hp , c th l nu pht hin
thy mt cch phn on t no khng ph hp ( khng c trong t in , khng c phi
l t ly , khng phi l danh t ring ,) th tc gi loi b cc nhnh xut pht t
cch phn on on .o Bc 3: La chn kh nng phn on t ti u : Sau khi c c
danh sch cc cch phn on t c th c ca cu , tc gi chn trng hp phn on t
c trng s b
nht.__________________________________________________________________________Hc
vin : Trnh Quc Sn-CH040104714Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit 3.2 Tng mng Neural : M hnh c s dng kh nhp nhng khi
tch t bng cch kt hp so snh vi t in.Nhn xt : M hnh ny t c chnh xc
trn 97% theo nh cng b trong cng trnh ca tc gi , bng vic s dng thm
mng Neural kt hp vi t in kh cc nhp nhng c th c khi tch ra cc c nhiu
t t mt cu v khi tng mng Neural s loi b i cc t khng ph hp bng cch kt
hp vi t in. Bn cnh , cng tng t nh phng php TBL im quan trng ca m
hnh ny cn tp ng liu hc y .III.4.Phng php tch tch t ting Vit da trn
thng k t Internet v thut gii di truyn Phng php tch tch t ting Vit
da trn thng k t Internet v thut gii di truyn IGATEC (Internet and
Genetics Algorithm based Text Categorization for Documents in
Vietnamese) do H. Nguyn xut nm 2005nh mt hng tip cn mi trong tch t
vi mc ch phn loi vn bn m khng cn dng n mt t in hay tp ng liu hc no
. Trong hng tip cn ny , tc gi kt hp gia thut ton di truyn vi d liu
thng k c ly t Internet .Trong tip cn ca mnh , tc gi m t h thng tch
t gm cc thnh phn a. Online Extractor : Thnh phn ny c tc dng ly thng
tin v tn s xut hin ca cc t trong vn bn bng cch s dng mt search
engine ni ting nh Google hay Yahoo chng hn . Sau , tc gi s dng cc
cng thc di y tnh ton mc ph thuc ln nhau (mutual information) lm c s
tnh fitness cho GA engine. Tnh xc sut cc t xut hin trn Internet :
__________________________________________________________________________Hc
vin : Trnh Quc Sn-CH040104715Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit ( )MAX)w2&w1count()w2&w1p(MAXcount(w)w p
Trong MAX = 4 * 109count(w) s lng vn bn trn Internet c tm thy c cha
t w hoc cng cha w1 v w2 i vi count(w1&w2). Tnh xc sut ph thuc
ca mt t ln mt t khc :( )w1p)w2&w1p()w2|w1p( Thng tin ph thuc ln
nhau (mutual information) ca cc t ghp c cu to bi n ting ( cw =
w1w2wn)( )n1 j)wn& ..... &w2&w1p(wjp)wn& .....
&w2&w1p(MI(cw)b. GA Engine for Text Segmentation : mi c th
trong quan th c biu din bi chui cc bit 0,1 , trong , mi bit i din
cho mt ting trong vn bn , mi nhm bit cng loi i din cho cho mt
segment. Cc c th trong qun th c khi to ngu nhin , trong mi segment
c gii hn trong khong 5 . GA engine sau thc hin cc bc t bin v lai
ghp nhm mc ch lm tng gi tr fitness ca cc c th t c cch tch t tt nht
c th.IV. KT LUN : Sau khi xem xt mt s hng tip cn trong tch t vn bn
ting Vit , cc nghin cu c cng b u ch ra rng phng php tch t da trn t
mang li kt qa c chnh xc kh cao , iu ny c c nh vo tp hun luyn ln , c
nh du ranh gii gia cc t chnh xc gip cho vic hc rt ra cc lut tch t
cho cc vn bn
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vin : Trnh Quc Sn-CH040104716Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit khc c tt p , tuy nhin chng ta cng d nhn thy hiu sut
ca phng php hon ton ph thuc vo tp ng liu hun luyn. Do khc phc s ph
thuc ca t in, chng ta ngh s dng hng tip cn ca H.Nguyn (s c trnh by
chi tit trong phn sau ) tch t .Hng tip cn da trn k t c u im l d thc
hin , thi gian thc hin tng i nhanh , tuy nhin li cho kt qa khng
chnh xc bng hng tip cn da trn t . Hng tip cn ny ni chung ph hp cho
cc ng dng khng cn chnh xc tuyt i trong tch t vn bn nh ng dng lc
spam mail , firewall ,Nhn chung vi hng tip cn ny nu chng ta c th ci
tin nng cao chnh xc trong tch t th hng tip cn ny l hon ton kh thi v
c kh nng thay th hng tip cn tch t da trn t v khng phi xy dng kho ng
liu , mt cng vic i hi nhiu cng sc , thi gian v s h tr ca cc chuyn
gia trong cc lnh vc khc nhau.CHNG 4 : PHN LOI VN BN TING VIT tin
hnh phn loi vn bn ni chung, chng ta s thc hin cc bc nh sau : Bc 1 :
Rt trch c trng vn bn v biu din vn bn bng m hnh
vector.__________________________________________________________________________Hc
vin : Trnh Quc Sn-CH040104717Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit Bc 2 : p dng thut ton phn loivn bn . Bc ny chng ta s
xut s dng thut ton Navie Bayes phn loi vn bn v nhn chung y l mt
thut ton phn loi tuyn tnh thch hp trong phn loi vn bn nhiu ch . NB
c u im l ci t n gin , tc thc hin thut ton nhanh , d dng cp nht d
liu hun luyn mi v c tnh c lp cao vi tp hun luyn .I.RT TRCH C TRNG
VN BNV BIU DIN BNG M HNH VECTOR rt trch c trng ca vn bn , chng s
thc hin thao tc tch t trong vn bn , xc nh t loi ca t v sau tin hnh
biu din cc vn bn bng m hnh vector .I.1.Tch t trong vn bn : Phng php
tch tch t ting Vit da trn thng k t Internet v thut gii di truyn
IGATEC (Internet and Genetics Algorithm based Text Categorization
for Documents in Vietnamese) do H. Nguyn xut nm 2005nh mt hng tip
cn mi trong tch t vi mc ch phn loi vn bn m khng cn dng n mt t in
hay tp ng liu hc no . Trong hng tip cn ny , tc gi kt hp gia thut
ton di truyn vi d liu thng k c ly t Internet .Trong tip cn ca mnh ,
tc gi m t h thng tch t gm cc thnh phn 1.1 Online Extractor : Thnh
phn ny c tc dng ly thng tin v tn s xut hin ca cc t trong vn bn bng
cch s dng mt search engine ni ting nh Google hay Yahoo chng hn .
Sau , tc gi s dng cc cng thc di y tnh ton mc ph thuc ln nhau
(mutual information) lm c s tnh fitness cho GA engine. Tnh xc sut
cc t xut hin trn Internet : (
)MAX)w2&w1count()w2&w1p(MAXcount(w)w p Trong : MAX = 4 *
109__________________________________________________________________________Hc
vin : Trnh Quc Sn-CH040104718Kha Lun Mn DataMiningNghin Cu Phn Loi
Vn Bn Ting Vit count(w) s lng vn bn trn Internet c tm thy c cha t w
hoc cng cha w1 v w2 i vi count(w1&w2). Tnh xc sut ph thuc ca mt
t ln mt t khc :( )w1p)w2&w1p()w2|w1p( Thng tin ph thuc ln nhau
(mutual information) ca cc t ghp c cu to bi n ting ( cw = w1w2wn)(
)n1 j)wn& ..... &w2&w1p(wjp)wn& .....
&w2&w1p(MI(cw)1.2 GA Engine for Text Segmentation : mi c th
trong quan th c biu din bi chui cc bit 0,1 , trong , mi bit i din
cho mt ting trong vn bn , mi nhm bit cng loi i din cho cho mt
segment. Cc c th trong qun th c khi to ngu nhin , trong mi segment
c gii hn trong khong 5 . GA engine sau thc hin cc bc t bin v lai
ghp nhm mc ch lm tng gi tr fitness ca cc c th t c cch tch t tt nht
c th.1.2.1 Khi to qun th:a. Biu din c th :Gi s vn bn u vo t bao gm
n ting nh sau : T=s1s2sn .Mc ch ca qa trnh thc hin thut ton GA l tm
cch tch ra cc t c ph hp cao nht : t=w1w2wm vi wk =sisj ( 1
