Lng Qu Tnh H Kha 3

LI CM N

Trong sut qu trnh thc hin lun vn, ngoi n lc chnh bn thn, ti cn nhn c rt nhiu ngun ng vin cng nh nhiu s gip t cc thy, cc c,

bn b v gia nh. y l mt trong nhng ngun ng lc v cng to ln ng hnh cng ti v gip ti hon thnh chng trnh hc cng nh lun vn ny. V vy,

ti xin by t lng bit n chn thnh n:

Thy TS. Nguyn Tun ng - ngi hng dn khoa hc nghim tc v nhit tm, hng dn, nh hng v truyn t cho ti nhng kin thc chuyn mn cng nh nhng kinh nghim qu bu trong nghin cu khoa hc v ng thi to mi iu kin cho ti trong sut thi gian thc

hin ti.

Cc thy, c trong khoa Khoa Hc My Tnh thuc trng i Hc Cng

Ngh Thng Tin, TP. HCM lun h tr kinh nghim, chia s nhng

kh khn trong cng vic v ng vin ti.

Bn Hunh Nguyn Pht v cc anh ch cao hc kho 3 gip ti trong lc thc hin ti.

Ba, M v em dnh cho con mt tnh thng v b bn, mt ngun ng lc v l ch da tinh thn vng chc nht gip con hon thnh lun vn ny.

TP. H Ch Minh, thng 11 nm 2009 Lng Qu Tnh H

Lng Qu Tnh H Kha 3

1

DANH MC HNH

Hnh 1.1 Kin trc phn tng ca web ng ngha ....................................................... 13 Hnh 2.1 Lc b ba (resource, property, value) ca RDF .................................... 24 Hnh 2.2 Biu din b ba (resource, property, value) di dng XML ...................... 25 Hnh 2.3 S phn cp lp ............................................................................................ 34

Hnh 2.4 Cc lp RDF v RDFS ................................................................................. 37

Hnh 2.5 Hai b ba RDF .............................................................................................. 38 Hnh 2.6 M hnh b ba (?album, music:author, ?author) ca RDF ........................... 38 Hnh 2.7 Lc RDF phc tp ................................................................................. 39 Hnh 2.8 Lc SPARQL phc tp .......................................................................... 40 Hnh 2.9 S hnh thnh OWL ...................................................................................... 42 Hnh 2.10 Mi quan h ca lp con gia OWL v RDF/RDFS .................................. 45 Hnh 2.11 Cc thuc tnh o ...................................................................................... 48

Hnh 3.1 M hnh h thng .......................................................................................... 94 Hnh 3.2 Cc thnh phn ca h thng ........................................................................ 95 Hnh 3.3 Cy c php sau khi phn tch v d 1 .......................................................... 97 Hnh 3.4 Thc hin nh x ln nt thuc cy c php .............................................. 100

Hnh 3.5 Cy sinh m truy vn .................................................................................. 101 Hnh 3.6 Lung d liu ca thnh phn phn tch cu hi ........................................ 103 Hnh 3.7 S thnh phn phn tch cu hi ............................................................ 105 Hnh 3.8 S thnh phn nh x ontology ............................................................. 107

Hnh 3.9 Cy sinh m ................................................................................................ 110 Hnh 3.10 Cc lp thuc thnh phn sinh m ............................................................ 111

Hnh 3.11 S thnh phn xy dng ontology v truy vn .................................... 116 Hnh 3.12 S cc lp chnh ................................................................................... 118

Hnh 4.1 Giao din chng trnh ............................................................................... 120

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DANH MC BNG

Bng 2.1 C php v ng ngha ca cc hm to lp (constructor) thng dng ......... 73 Bng 2.2 C php tng minh v tru tng ca cc constructor khi nim ............. 74

Bng 2.3 C php v ng ngha ca cc constructor lut thng dng ........................ 75 Bng 2.4 C php tng minh v tru tng ca cc constructor lut ....................... 76 Bng 2.5 C php v ng ngha ca cc tin xc nhn v thut ng ..................... 77

Lng Qu Tnh H Kha 3

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MC LC

CHNG I - TNG QUAN ..................................................................................... 6 1.1 t vn ............................................................................................................ 6 1.2 Phm vi nghin cu .............................................................................................. 7

1.2.1 Gii hn vn nghin cu .................................................................................. 7

1.2.2 ngha khoa hc ................................................................................................... 7 1.3 Hin trng nghin cu .......................................................................................... 7

1.3.1 Tnh hnh nghin cu trn th gii ...................................................................... 7

1.3.2 Tnh hnh nghin cu ti Vit Nam ..................................................................... 9

CHNG II - C S L THUYT ..................................................................... 11 2.1 i tng nghin cu ....................................................................................... 11

2.2 Phng php nghin cu.................................................................................... 11

2.2.1 Phng php xy dng ontology ....................................................................... 11 2.2.1.1 Ontology ........................................................................................................ 15

A. Thut ng ontology .......................................................................................... 15

B. nh ngha ontology ......................................................................................... 15

C. Thnh phn ca ontology ................................................................................ 15

D. Ti sao cn xy dng Ontology? .................................................................... 16 E. Xy dng ontology nh th no? .................................................................... 17 F. Kt lun .............................................................................................................. 22

2.2.1.2 Cc ngn ng ontology cho web ................................................................ 23 A. RDF v RDF Schema ...................................................................................... 23

B. Ngn ng ontology web (OWL) .................................................................... 41 2.2.1.3 Logic v suy din .......................................................................................... 60

A. Gii thiu ........................................................................................................... 60

B. Cc lut n iu .............................................................................................. 60

C. Lut khng n iu ........................................................................................ 63 D. Biu din cc lut n iu trong XML ........................................................ 64

Lng Qu Tnh H Kha 3

4

E. Biu din cc lut khng n iu trong trong XML .................................. 68 F. Kt lun .............................................................................................................. 68

2.2.1.4 Logic m t.................................................................................................... 69

A. Gii thiu ........................................................................................................... 69 B. C php v ng ngha ca logic m t........................................................... 69

C. Nn tng tri thc ............................................................................................... 77

D. Suy din ............................................................................................................. 81 E. Lut ..................................................................................................................... 85

2.2.2 Phng php phn tch cu ting Vit bng ngn ng BNF/EBNF ............. 88 2.2.2.1 Ngn ng BNF .............................................................................................. 88

A. Gii thiu ........................................................................................................... 88 B. C php ca BNF ............................................................................................. 89

2.2.2.2 Ngn ng EBNF ........................................................................................... 90

A. Gii thiu ........................................................................................................... 90

B. C php ca EBNF ........................................................................................... 90

2.2.2.3 So snh ngn ng BNF v EBNF............................................................... 92

2.2.2.4 Mt s chng trnh x l ngn ng BNF/EBNF.................................... 92

CHNG III - XY DNG CHNG TRNH ................................................. 93 3.1 M hnh h thng ............................................................................................... 93

3.1.1 Bn thnh phn ca h thng ............................................................................. 94

3.1.2 Hai lung d liu chnh ca h thng ............................................................... 94 3.2 Cc thnh phn ca h thng ............................................................................. 94

3.2.1 Thnh phn phn tch cu hi ............................................................................ 95 3.2.1.1 D liu vo v ra ca thnh phn ............................................................... 95

3.2.1.2 Cc t kho .................................................................................................... 95

A. Cu hi ting Vit ............................................................................................ 96

B. Cy c php ....................................................................................................... 96

C. Cy sinh m truy vn ....................................................................................... 98

3.2.1.3 Lung d liu .............................................................................................. 103 3.2.1.4 S cc lp chnh .................................................................................... 104

Lng Qu Tnh H Kha 3

5

A. Thnh phn phn tch cu hi ....................................................................... 104

B. Thnh phn nh x ontology ......................................................................... 106

3.2.2 Thnh phn sinh m SPARQL ......................................................................... 108 3.2.2.1 D liu vo v ra ca thnh phn ............................................................. 108 3.2.2.2 Gii hn xem xt cu hi ting Vit ........................................................ 108

3.2.2.3 Lung d liu .............................................................................................. 111 3.2.2.4 S cc lp chnh m t ......................................................................... 111

3.2.3 Thnh phn xy dng ontology v truy vn ................................................... 112 3.2.3.1 D liu vo v ra ca thnh phn ............................................................. 112

3.2.3.2 Cu trc ontology ....................................................................................... 112

A. Cc lp ontology ............................................................................................ 112 B. M t thng tin tng lp ................................................................................ 113

3.2.3.3 Lung d liu .............................................................................................. 114 3.2.3.4 S cc lp chnh .................................................................................... 114

3.2.4 Thnh phn rt trch thng tin .......................................................................... 117

3.2.4.1 D liu vo v ra ca thnh phn ............................................................. 117

3.2.4.2 S cc lp chnh .................................................................................... 117

CHNG IV - TH NGHIM ............................................................................ 119 4.1 Ci t .............................................................................................................. 119 4.2 Th nghim d liu .......................................................................................... 120 4.3 nh gi h thng ............................................................................................ 121

CHNG V - KT LUN V HNG PHT TRIN ................................. 122 5.1. Kt qu t c v nhng ng gp chnh trong lun vn ........................... 122 5.2 Nhng kh khn v hn ch ............................................................................. 122 5.3 Cc hng pht trin ........................................................................................ 122

TI LIU THAM KHO ...................................................................................... 123

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CHNG I - TNG QUAN

1.1 t vn Hin nay cng ngh phc v cho my tnh ngy cng pht trin nhanh chng, c

bit l internet, v em li nhiu li ch to ln cho con ngi. Song song vi s pht trin , th lng thng tin cng ngy cng ln dn ln v nhu cu tm kim thng tin trn internet cng ngy cng gia tng. p ng nhu cu tm kim ,

hng lot cc cng c tm kim ra i (google, yahoo, Teoma). Tuy nhin, hin nay hu ht cc cng c tm kim ch yu tm kim da trn t kha hay mt cm t nhp vo, v cng c mt s cng c tm kim c tm kim phn loi theo ch [7].

V hu ht cc cng c tm kim ch yu da trn t kha hay cm t nn khi thc hin vic tm kim s cho ra rt nhiu trang web cha t kha hay cm t . V vy, c c thng tin chnh xc m ngi tm kim cn th h cng phi tn rt

nhiu thi gian duyt rt nhiu trang web c cha cc t kha hay cm t , i khi khng th tm c thng tin cn thit (do thng tin b n) bi v do bn quyn ca bi bo hay trang web.

Mc d c rt nhiu cng c tm kim (da trn t kha l ch yu) nhng cng c tm kim h tr cho ting Vit hu nh rt t, cho kt qu tm kim cn hn

ch. V vy, vic tm kim thng tin chnh xc, c bit l tm kim cho ting Vit, l nhu cu v mc ch cui cng ca ngi tm kim. p ng mc ch ny, chng

ti thc hin ti:

Xy dng cng c tm kim ti liu hc tp bng cc truy vn ngn ng t nhin trn kho hc liu m ting Vit

ti ny khng thc hin vic tm kim da trn t kho hay cm t v khng tr v cc trang web cha t kho hay cm t, m tr v cu tr li tng ng vi nhng cu hi do ngi dng nhp vo. Ni cch khc, khi ngi dng nhp cu hi bng ting Vit, th cng c tm kim tr v cu tr li chnh xc cho thng tin ngi dng.

Lng Qu Tnh H Kha 3

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1.2 Phm vi nghin cu 1.2.1 Gii hn vn nghin cu

Mc tiu ca lun vn cho php ngi dng nhp cu hi bng ting Vit v h thng tr v cu tr li. Cu hi ngi dng ch gm cc vn lin quan n kho hc: tn (name), m (id), ngn ng (language), tm tt (summary), t kha (keywords), loi ti liu (document type), bn quyn (license), tc gi (authors), chu trch nhim xut bn (copyright holders), chnh l (maintainers), phin bn (version), ngy to (created), ngy chnh sa (revised).

Cu tr li tr v thng tin thuc kho hc liu m Vit Nam (www.vocw.edu.vn). 1.2.2 ngha khoa hc

p ng c nhu cu tm kim thng tin chnh xc.

Vic tm kim thng tin chnh xc khng da trn t kho hay cm t m da trc tip vo cu hi ting Vit ca ngi dng tr li chnh xc cho cu hi .

1.3 Hin trng nghin cu 1.3.1 Tnh hnh nghin cu trn th gii

Trn th gii hin nay, c rt nhiu cng c tm kim hu nh da trn t kha ra i nh google, yahoo, msn, alibaba V kt qu tm kim cng phn no lm tha mn nhu cu tm kim i vi ngi dng mc d phn ln tn nhiu thi gian duyt qua.

Tuy nhin, cng c tm kim lin quan n vic hi-p (ng ngha) tr li chnh xc cu hi ca ngi dng th khng nhiu.

Mt s cng c tm kim nc ngoi [7]:

Cng c tm kim C s d liu T kha hay hi-p (ng ngha)

Kh nng tm kim

Google www.google.com

Ton b vn bn cc trang web, pdf, MS.Office, PostScript

T kha

- H tr tm kim

nng cao.

- Dng * rt gn

(thay th t trong cm t). - Dng du

Lng Qu Tnh H Kha 3

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tm cm t.

- Tm theo vng.

- Tm cc trang lin

quan.

- Tm hnh nh

- Tm kim theo

nhiu ngn ng.

AllTheWeb www. allTheWeb.com

Ton b vn bn ca cc trang web, PDF, MS

Office,

PostScript

.

T kha

- Khng rt gn,

dng tm cm t - Tm theo vng.

- Tm hnh nh v

video

AltaVista www.altavista.com

Ton b vn bn ca cc trang web.

T kha

- Dng tm cm

t .

- Dng * rt gn.

- Phn bit ch hoa, ch thng.

- T ng xc nh

cm t v kim tra

chnh t.

- Tm hnh nh, m

thanh, video v tin tc.

- Tm kim theo

nhiu ngn ng

khc nhau.

Teoma

teoma.com

Ton b vn bn ca cc trang web.

T kha

- Khng rt gn

- Dng tm cm

t .

- Tm kim theo cc

Lng Qu Tnh H Kha 3

9

gii hn nh ngy,

ngn ng, v tr,

su lin kt ca

trang WEB.

- C th gom nhm cc kt qu.

Ixquick www.ixquick.com

Searches

AltaVista,

Ask Jeeves

/Teoma,

MSN, Yahoo

& more.

T kha

- H tr tm kim tin

tc, file mp3, file

nh.

- Tp hp v phn

hng cc kt qu,

hn ch s trng lp

thng tin.

AskJeeves www.ask.com

p ng hng

triu cc yu

cu t cc site

c lng.

T kha

- Dng du nhy kp tm kim

cm t trong

Teoma.

- Hot ng hiu

qu i vi cc yu

cu n gin.

1.3.2 Tnh hnh nghin cu ti Vit Nam Vn tm kim l mt trong nhng vn rt quan trng khi tm ti liu mong

mun. Mc d hin nay trn th gii xut hin rt nhiu cng c tm kim h tr nhiu ngn ng nhng Vit Nam, cng c tm kim h tr cho ting Vit khng

nhiu, c bit l cng c tm kim theo ng ngha. Tuy vy, cng c mt s cng c tm kim ra i nh NetNam, VinaSeek,

ZingSearch cng gp mt phn no trong vic tm kim da trn t kha ting Vit.

Lng Qu Tnh H Kha 3

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Mt s cng c tm kim trong nc [7]:

Cng c tm kim C s d liu T kha hay hi-p

(ng ngha) Kh nng tm

kim

NetNam www.pan.vietnam.

com

Ton b vn bn ca cc trang

web.

T kha

- Dng tm cm

t .

- Phn bit ch hoa v thng.

- S dng t kha lc cc.

VinaSeek www.vinaseek.

com Tm kim.

Ton b vn bn ca cc trang

web.

T kha

- Dng tm cm

t .

- Phn bit ch hoa v thng.

- S dng t kha lc cc tm

kim.

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CHNG II - C S L THUYT

2.1 i tng nghin cu Thng tin t trang hc liu m (www.vocw.edu.vn). Trang hc liu m cha cc kha hc. Vo thi im 11/8/2009, trang hc liu

cha 225 kha hc (course). Mi kha hc u cha thng tin metadata bao gm: Tn (Name) M (ID) Ngn ng (Language) Tm tt (Summary) T kha (Keywords) Loi ti liu (Document Type) Bn quyn (License) Tc gi (Authors) Chu trch nhim xut bn (Copyright Holders) Chnh l (Maintainers) Phin bn (Version) Ngy to (Created) Ngy chnh sa (Revised)

V mi tc gi u c trang cha thng tin c nhn. Thng tin trong trang c

nhn c th cha trng d liu: n v cng tc (a ch lin lc) ca tc gi Cu hi ting Vit

Xt cc cu hi bng ting Vit lin quan n cc thnh phn thuc i tng thng tin (metadata, tc gi) t trang hc liu m.

2.2 Phng php nghin cu 2.2.1 Phng php xy dng ontology

Hu ht thng tin ca web hin ti hu nh khng c cu trc v vn cn nhiu hn ch trong vic tm kim thng tin (da trn t kha), rt trch thng tin (tn nhiu thi gian duyt), bo tr thng tin (thng tin li thi v cc mu thun gia cc

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12

thut ng khng th loi b), khm ph thng tin (thu thp thng tin) v xem thng tin (b qua nhng thng tin h thng web chnh l web ng ngha, nhm to ra nhng h thng qun l tri thc tin tin hn). V vy, cn c mt h thng web mi ra i khc phc nhng hn ch trn:

Tri thc s c t chc theo cc khi nim v ng ngha ca n.

Cc cng c t ng s h tr vic bo tr bng cch kim tra nhng mu thun v rt trch tri thc mi.

Thay th vic tm kim da trn t kha bng vic tr li cu hi (hi-p): nhng tri thc c yu cu s c rt trch, ly ra v biu din theo cch thun li nht cho con ngi.

Hi-p i vi mt vi ti liu s c h tr.

C th xc nh ngi m xem mt phn thng tin (thm tr mt phn ti liu).

S pht trin web ng ngha din ra theo tng bc, mi bc xy dng nn mt tng nm trn tng khc. Trong qu trnh xy dng mt tng web ng ngha, cn tun theo 2 nguyn tc:

Tnh tng thch t trn xung (downward compatibility): cc tc t (Agent) nhn bit hon ton mt tng cng c th suy din v s dng thng tin c vit mc thp hn. V d, cc Agent hiu ng ngha ca OWL c th s dng cc thng tin c vit trong RDF v RDF Schema.

S thng hiu tng phn t di ln (upward partial understanding): cc Agent nhn bit hon ton mt tng th t nht c th s dng mt phn thng tin mc cao hn. V d, Agent ch hiu RDF v ng ngha RDF Schema c th biu din tri thc c vit mt phn no trong OWL.

Hnh 1 l kin trc phn tng ca web ng ngha (do Tim Berners-Lee ra) m t nhng tng chnh v vic thit k web ng ngha:

Lng Qu Tnh H Kha 3

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Hnh 1.1 Kin trc phn tng ca web ng ngha (Ngun t: A Semantic web Primer (2004), Grigoris Antoniou and Frank van Harmelen, page 18, figure 1.3)

Tng XML: mt ngn ng cho php to ra cc ti liu web c cu trc vi t vng do ngi dng nh ngha. XML ph hp vi vic gi cc ti liu thng qua web.

Tng RDF v RDF Schema: RDF l m hnh d liu c bn nhm vit cc pht biu c bn v cc i tng web. M hnh d liu RDF khng da trn XML, nhng RDF c c php da trn XML. RDF Schema c xem l ngn ng c bn vit ontology. Tuy nhin, cng cn c nhiu ngn ng ontology m rng mnh hn biu din cc mi quan h phc tp hn gia cc i tng web.

Tng Ontology vocabulary (ontology): cung cp b t vng chung, kh nng biu din ng ngha cho ti nguyn web v kh nng h tr lp lun.

Tng Logic: dng tng cng ngn ng ontology hn v cho php vit cc tri thc khai bo ng dng chuyn bit (application-specific declarative knowledge).

Tng Proof: lin quan n qu trnh suy din s tht cng nh s biu din cc Proof trong ngn ng web (t cc lp thp hn) v s xc nhn tnh hp l ca Proof.

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Tng Trust: s dng cc k hiu k thut s (digital signatures) v nhng loi tri thc khc. i khi web Trust c s dng biu din Trust c s sp xp theo cch hn n v c sp xp theo mt kiu nht nh nh

chnh WWW. Trust l mc cao nht v l khi nim ct yu.

Lng Qu Tnh H Kha 3

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2.2.1.1 Ontology [1][2][3]

A. Thut ng ontology

T ontology c ngun gc t ting Hy Lp: ontos ngha l being (tn ti, sng, thc s) v logos ngha l word (t) [1]. Trong trit hc, ontology thuc mt lnh vc nh ca trit hc, nghin cu v s tn ti ca t nhin, ch yu xc nh nhng

thut ng thng dng nht, nhng th tn ti thc s, v bng cch no m t chng [2].

B. nh ngha ontology

Trong tr tu nhn to v trong tin hc cng nh trong khoa hc my tnh, c rt

nhiu nh ngha v ontology, nhng mt trong nhng nh ngha sc tch nht, l

theo T.R. Gruber (An ontology is an specification of a conceptualization) [1], sau c ci tin bi R. Studer: ontology l mt s c th ha hnh thc v tng minh ca tru tng ha (An ontology is an explicit and formal specification of a conceptualization) [2]. Tru tng ha (conceptualization) c ngha l mt nim tru tng (abstract), mt quan im n gin ha ca th gii. Cn c th ha (specification) c ngha l mt s biu din khai bo v hnh thc. Trong cu trc d liu, vic biu din ontology, cc khi nim v cc rng buc cn phi c khai bo, tng minh v c s dng ngn ng hnh thc [1].

Thng th khi ni n ontology l ni n mt ontology. Mt ontology l mt

m hnh d liu biu din mt lnh vc (min), v dng n suy lun v cc i tng trong lnh vc v mi quan h gia chng [2].

C. Thnh phn ca ontology

Ontology cung cp mt b t vng (terminology) chung bao gm cc khi nim (thut ng), cc thuc tnh (property) quan trng, cc nh ngha v cc khi nim v cc thuc tnh ny, v mi quan h gia chng. Mi quan h thng gm cc phn

cp lp. Mt phn cp ch r mt lp C l lp con ca lp C khc nu mi i tng

trong C cng u thuc trong C. Ngoi ra, ontology cn cung cp cc rng buc, v cc rng buc ny c th c xem nh cc gi nh nn tng ca b t vng v c s dng trong mt min no [2].

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B t vng ca ontology c xy dng da trn tng RDF v RDFS trong kin trc phn tng ca web ng ngha. N cung cp kh nng biu din ng ngha cho ti nguyn web v c kh nng h tr lp lun [2].

C th (individual): c th c th l cc i tng c th nh con ngi, ng vt, ci bn cng nh cc c th tru tng nh cc thnh vin hay cc t. Mt ontology c th khng cha c th no.

Lp (class): l mt nhm, tp hp cc i tng, c th cha cc c th, cc lp khc. Mt lp c th cha cc lp con, c th l mt lp tng qut (cha mi th), hoc ch cha cc c th ring l. Mt lp c th xp gp hoc c xp gp vo cc

lp khc.

Thuc tnh (property): dng m t cc i tng trong ontology. Mi mt thuc tnh u c tn v gi tr ca thuc tnh . Thuc tnh dng lu tr cc thng tin ca i tng. Gi tr ca mt thuc tnh c th l cc kiu d liu phc tp.

Mi lin h (relationship): l mt thuc tnh ca mt i tng no trong ontology. Lp ny c th gp vo lp kia to nn mt kiu quan h xp gp, cho bit i tng no l thnh vin ca lp no.

D. Ti sao cn xy dng Ontology? [1][2][3]

V ontology cung cp b t vng chung cha nhng thng tin (d liu) c cu trc v mt min no , c kh nng biu din ng ngha cho ti nguyn web, c kh nng h tr lp lun, v thng tin (d liu) ca ontology my c th hiu v x l c, ngha l ontology cung cp mt kin trc quan trng cho vic chuyn web ca thng tin v d liu sang web ca tri thc (web ng ngha), nn cn phi xy dng ontology c th:

Chia s hiu bit cu trc ca thng tin gia ngi dng vi nhau hoc gia cc ng dng

Ti s dng min tri thc no

To ra min d liu r rng, n gin, d nh v d s dng

Phn tch, rt trch thng tin trong min tri thc no

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17

E. Xy dng ontology nh th no? [2][3]

Pht trin mt ontology thng l mt quy trnh lp li. Nn tng xy dng b t vng ontology l tng RDF v RDF Schema (RDFS).

Cc bc xy dng ontology:

Xc nh min (domain) v phm vi (scope) ca ontology

Pht trin mt ontology ging nh nh ngha mt b d liu v cu trc ca chng cho chng trnh khc s dng. V ontology l mt m hnh ca mt min c th, c xy dng vi mc ch c th.

Nhng cu hi c bn phi tr li trong bc ny:

Min m ontology s cha l g?

Chng ta s dng ontology vi mc ch g?

Ontology cung cp cc cu tr li cho nhng loi cu hi no?

Ai s s dng v bo tr ontology?

Xem xt s ti s dng cc ontology tn ti

Vic xem xt cc ontology c cng rt quan trng, gip chng

ta c th lc v m rng cc ngun c cho mc ch to

ontology ca chnh chng ta. Ngoi ra, vic ti s dng ontology c i khi rt cn thit khi h thng chng ta cn tng tc vi

cc ng dng khc.

Chng ta c th ti s dng cc ontology sn c trong cng mt min min sao ph hp vi mc ch to ontology ca chng ta.

Hn na, vic chuyn mt ontology t dng ny sang dng khc th thng khng d. Do , vic xem xt ti s dng cc ontology c sn gip tit kim thi gian xy dng ontology ca chng ta.

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Tuy nhin, nu ontology khng c sn, chng ta phi to ra

ontology mi.

Lit k cc thut ng quan trng

Xc nh cc thut ng c lin quan.

Vit ra mt danh sch cc thut ng lin quan cha c cu trc. Thng th cc danh t cho tn lp (class), ng t (hoc cm ng t) cho tn thuc tnh (property), chng hn nh is part of, has component.

Xc nh cc mi quan h gia cc thut ng, phn cp cc lp

v nh ngha cc thuc tnh ca cc khi nim c quan h vi

nhau.

Xc nh lp v phn loi lp (taxonomy)

Sp xp, phn loi cc thut ng c lin quan theo cp bc, theo nhm, c th theo m hnh t trn xung (top-down) hoc t di ln (bottom-up) hoc phi hp c hai (combination).

M hnh top-down: s bt u t vic nh ngha cc khi nim chung nht, k n l c th ca cc khi nim. V d nh, lp ru vang (wine) l mt khi nim chung nht, cn cc ru vang trng (white wine), ru vang hng (rose wine) v ru vang (red wine) l lp con ca cc khi nim c th. Nh vy, ru vang (wine) s cha (gm) cc ru vang trng, vang hng v vang .

M hnh bottom-up: s bt u vi vic nh ngha cc lp c th nht, sau nhm cc lp ny li thnh nhng khi nim chung

hn. V d nh, u tin chng ta nh ngha 2 lp ru: lp ru vang Pauillac v Margaux. Sau , to ra mt siu lp

(superclass) chung cho 2 lp ny l Medoc.

M hnh kt hp (combination): y l m hnh kt hp gia m hnh top-down v bottom-up. u tin, chng ta nh ngha cc

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khi nim ni bt hn. Sau , khi qut ha v c th ha chng tng ng mt cch ph hp. Chng ta c th bt u vi mt vi khi nim mc nh (top) (v d nh wine) v mt vi khi nim c th (v d nh Margaux). Sau , chng ta ni chng vi mt khi nim mc trung (middle) (v d nh Medoc). Nh vy, chng ta to ra cc lp ru vang v cng to ra nhiu khi nim

mc trung.

Ty vo mc ch c th m c th s dng thch hp cc m hnh trn, c th s dng mt m hnh hoc kt hp nhiu m hnh li vi nhau.

Chng ta c th phn cp cc thut ng thnh cc lp. Sau , cc lp ny tip tc c phn cp (phn cp lp). Tuy nhin, s phn cp ny cn tun theo: nu mt lp A l mt lp cha

(superclass) ca lp B, th mi thc th (instance) ca B cng l thc th ca A.

Xc nh cc thuc tnh (properties)

Khi chng ta nh ngha mt vi lp, chng ta phi m t cu trc

bn trong ca cc khi nim.

i vi mi thuc tnh, chng ta phi xc nh n m t lp no.

Cc thuc tnh ny c th l nhng thuc tnh c gn vo cc

lp. Thng thng, c mt vi loi thuc tnh i tng nh

thuc tnh bn trong (intrinsic), thuc tnh bn ngoi (extrinsic).

Thuc tnh (slot/property) biu din cc mi quan h gia hai c th (individual). Thuc tnh lin kt c th ca min (domain) v c th ca phm vi (range).

C 3 loi thuc tnh:

Thuc tnh i tng (object property): lin kt c th (individual) ny vi c th khc. Cc loi thuc tnh i tng:

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Thuc tnh o (inverse): v d nh has_parent l o ca has_child.

Thuc tnh hm (functional): v d nh has_birth_mother.

Thuc tnh bc cu (transitive): v d nh has_anchestor.

Thuc tnh i xng (symmetric): v d nh has_sibling.

Thuc tnh kiu d liu (data type property): lin kt mt c th (individual) vi gi tr kiu d liu ca XML Schema hoc kiu nguyn th (literal) ca rdf. V d nh has_birth_of_date.

Thuc tnh ch thch (annotation property): c dng thm thng tin (metadata) vo cc lp, cc c th v thuc tnh kiu d liu hoc thuc tnh i tng.

Tt c cc lp con ca mt lp k tha thuc tnh ca lp . Mt

thuc tnh c th c gn vo lp tng qut nht (c th mang thuc tnh ).

Vic xc nh cc thuc tnh cn gip pht hin nhng mu thun,

nhng khi nim sai.

Xc nh cc facet (gii hn ca thuc tnh hay gii hn lut)

Facet c dng biu din thng tin v cc thuc tnh (slots), i khi cn c gi l cc gii hn lut.

Cc thuc tnh c th c cc facet khc nhau m t cc kiu gi

tr, cc gi tr c php, cc s ca gi tr (cardinality) v cc c tnh (feature) khc m thuc tnh c th nhn.

Mt s facet:

S ca gi tr (cardinality)

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Cardinality biu din s chnh xc ca gi tr c xc nhn cho thuc tnh ca lp , v n xc nh c bao nhiu gi tr m thuc tnh c.

Nhiu h thng ch phn bit gia cardinality n (nhiu nht mt gi tr) v cardinality a (bt k s gi tr no) (minimum cardinality v maximum cardinality). Minimum cardinality N c ngha l mt thuc tnh phi c t nht N gi tr. Maximun

cardinality M c ngha l mt thuc tnh c ti a M gi tr.

Kiu gi tr (value type)

Facet ca kiu gi tr m t kiu gi tr no c th cho

vo thuc tnh. Mt s cc kiu gi tr:

Kiu chui (String)

Kiu s (Number)

Kiu Boolean

Kiu lit k (Enumerated)

Kiu instance

nh ngha cc thc th (instances)

Thc th l i tng hoc c th ca lp. nh ngha mt

thc th ring bit ca mt lp, ta thc hin nh sau:

Chn mt lp.

To mt thc th ring bit ca lp .

Thay th bng cc gi tr thuc tnh.

Kim tra nhng bt thng (anomalies)

Nhm pht hin tnh khng nht qun (mu thun) trong chnh ontology hoc trong b thc th (set of instances). Nhng mu

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thun c th l: s khng tng thch vi nh ngha min v

phm vi (range) cho tnh bc cu (transitive), tnh i xng (symmetric) hay cc thuc tnh o, cc thuc tnh s gi tr, cc gi tr thuc tnh c th xung t vi cc gii hn ca domain v range.

Kim tra nhng bt thng c th bng b lp lun (reasoner): Pellet, Racer

Tuy nhin, trn thc t, vic pht trin ontology gm cc bc sau:

Xc nh cc lp trong ontology.

Sp xp cc lp theo cp bc, theo nhm (lp cha-lp con).

Xc nh cc thuc tnh v m t cc gi tr c php cho cc thuc

tnh ny.

Sp xp hon chnh cc gi tr ca cc thuc tnh cho cc thc th

(instances).

F. Kt lun [2]

Nh vy, cc ontology rt c ch cho s t chc v iu hng cc website. Ontology cng ci thin chnh xc trong vic tm kim trn web. Cc cng c tm kim c th tm nhng trang web ch lin lin n khi nim trong mt ontology thay v thu thp tt c cc trang web thng cha cc t kha rt m h, nhp nhng v khng chnh xc lm. Theo cch ny, nhng khc nhau v thut ng gia cc trang

web v nhng truy vn c th c khc phc.

Hn na, tm kim web c th tm c nhng thng tin c th v khi qut. Nu khng thnh cng trong vic tm kim cc ti liu quan tm khi t cu hi, th

cc cng c tm kim s ngh ngi dng t cu hi tng qut hn. Thm ch, my c th hiu c v thc hin cc truy vn trc gim bt thi gian p ng trong trng hp ngi dng chp nhn s ngh . Hoc nu c qu nhiu cu tr li c rt trch, th cc cng c tm kim c th a ra cc ngh c tnh chuyn

mn hn cho ngi dng.

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Tuy nhin, khng c mt ontology no ng cho mi min. Cht lng ca

ontology c xc nh thng qua cc ng dng s dng n.

2.2.1.2 Cc ngn ng ontology cho web [2]

XML: cung cp c php cho cc ti liu c cu trc nhng khng yu cu

ng ngha i vi cc ti liu ny web.

XML Schema: l ngn ng gii hn cu trc ca ti liu XML.

RDF: l m hnh d liu cho cc i tng (ti nguyn_resource) v cc mi quan h gia chng. y l mt ng ngha n gin cho m hnh d liu ny, v m hnh d liu ny c biu din trong c php ca XML.

RDF Schema: l ngn ng m t t vng m t cc thuc tnh (property) v cc lp (class) ca ti nguyn RDF, cng vi ng ngha cho cc phn cp khi qut ha ca cc lp v cc quan h .

OWL: l ngn ng m t t vng phong ph m t cc thuc tnh v cc

lp, cc mi quan h gia cc lp (nh disjointness), s ca gi tr (cardinality), tnh tng ng (equality), nh kiu thuc tnh, c tnh ca thuc tnh (i xng) v cc lp m.

A. RDF v RDF Schema

a. RDF (Khung m t ti nguyn)

a.1 Gii thiu

XML l mt siu ngn ng (metalanguage) ph bin nh ngha nh dng (markup). N cung cp c php d dng v mt b cng c nh b phn tch c php (parser) trao i d liu v siu d liu (metadata) gia cc ng dng nh s dng XML Schema. Tuy nhin, XML khng cung cp bt k ng ngha no ca d liu. V vy, cn c mt m hnh chun no biu din cc s kin ca ti nguyn web. M hnh chun l RDF v RDF Schema.

V c bn, RDF l mt m hnh d liu. l m hnh b ba i tng-thuc tnh-gi tr (object-attribute-value triple), c gi l mt pht biu (statement). Mi

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pht biu c biu din di dng mt ti nguyn (resource hoc object), mt thuc tnh (property/attribute) ca n v mt gi tr (value) ca thuc tnh. Gi tr c th l nguyn th (literal) hoc ti nguyn khc.

Mt s b ba resource-property-value ca RDF v lc tng ng vi cc b ba :

Hnh 2.1 Lc b ba (resource, property, value) ca RDF (Ngun t: Dragan Gasevic, Dragan Djuric, Vladan Devedzic (2006), Model Driven Architecture and Ontology

Development, fig.3.4, trang 84)

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Nhng b ba trn cng c th c biu din nh sau (c s dng c php ca XML):

Hnh 2.2 Biu din b ba (resource, property, value) di dng XML (Ngun t: Dragan Gasevic, Dragan Djuric, Vladan Devedzic (2006), Model Driven Architecture and

Ontology Development, fig.3.4, trang 84)

M hnh RDF ch cung cp mt c cu min c lp m t cc ti nguyn

ring l. N khng u tin ng ngha ca bt k min ng dng no, v cng khng to ra gi nh no v min c th no . RDF thng dng m t cc thc th ca cc ontology, trong khi RDF Schema m ha cc ontology.

a.2 Cc khi nim c bn

Ti nguyn (resource)

C th xem ti nguyn nh mt i tng, mt th m chng ta mun ni.

Ti nguyn c th l tc gi, sch, nh xut bn, a im, con ngi

Mi resource c mt URI (Universal Resource Identifier_b nh danh ti nguyn chung). Mt URI c th l mt URL (Unified Resource Locator_b nh v ti nguyn hp nht hoc a ch web) hoc mt vi loi trnh nh danh (identifier) khc. Thng thng, chng ta cho rng mt URI l trnh nh danh ca ti nguyn web.

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Thuc tnh (property)

Thuc tnh l mt kiu ti nguyn c bit, m t cc mi quan h gia cc ti nguyn, chng hn nh written by, age, title. Thuc tnh trong RDF cng c xc nh bi URI (nhng thc t l URL).

Cc pht biu (statement)

Cc pht biu xc nh thuc tnh ca ti nguyn. Mt pht biu l mt b ba i tng-thuc tnh-gi tr (object-attribute-value triple), gm mt ti nguyn, mt thuc tnh v mt gi tr. Gi tr c th l hoc ti nguyn hoc nguyn th (literal). Literal l cc gi tr nguyn t (atomic value) hoc chui (string).

a.3 C php ca RDF

C php ca RDF da trn c php ca XML. Ti liu RDF gm mt phn t rdf:RDF, ni dung (content) l s lng cc m t (descriptions).

Grigoris Antoniou Professor

David Billington Associate Professor

2

Michael Maher

Professor

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Khng gian tn (namespace) trong XML c s dng trong nhng mc ch chung; cn trong RDF, khng gian tn l ti liu RDF nh ngha ti nguyn, c s

dng trong vic nhp ti liu RDF, v cho php ti s dng ti nguyn bi ngi khc chn thm cc c tnh vo trong cc ti nguyn ny.

Thuc tnh rdf:about ca phn t rdf:Description c dng ch rng i tng v pht biu no c to ra c nh ngha ni khc.

Ni dung ca phn t rdf:Description c gi l cc phn t thuc tnh. V d nh, trong m t:

Knowledge Representation Grigoris Antoniou

Cc phn t thuc tnh ca m t phi c c mt cch lin tc.

Thuc tnh rdf:resource

c s dng trong trng hp c s trng tn ngu nhin. Thuc tnh rdf:resource dng phn bit cc trng hp c tn ging nhau nhng l nhng ngi khc nhau.

David Billington Associate Professor

Phn t rdf:Description

Cc phn t rdf:Description c th c lng vo nhau.

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Discrete Mathematics

David Billington Associate Professor

Phn t rdf:type

Cho php chng ta a mt vi cu trc vo ti liu RDF.

Discrete Mathematics

Phn t cha (container elements)

Cc phn t cha c dng thu thp cc ti nguyn hoc cc thuc tnh m chng ta mun to cc pht biu nh mt tng th. C 3 loi phn t cha c sn trong RDF:

rdf:Bag: phn t cha khng c th t, cha nhiu s kin (occurrence).

rdf:Seq: phn t cha c th t, cha nhiu s kin.

rdf:Alt: mt b cc la chn (alternative).

Ni dung ca cc phn t cha l nhng phn t c t tn l rdf:_1, rdf:_2

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V d:

Thay v rdf:_1, rdf:_2 ..., c th vit rdf:li.

a.4 Ng ngha tin cho RDF

my c th s dng c (machine accessible) ng ngha tng minh, chng ta cn to ra ng ngha , m t ng ngha ca RDF trong ngn ng hnh thc ging

nh logic, v cung cp mt b lp lun (reasoner) t ng x l cc cng thc logic.

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Gii thiu

Tt c cc t mu (primitives) trong RDF c biu din bi cc hng (constant): Resource, Class, Property, subClassOf Mt vi v t c sn c s dng biu din cc mi quan h gia chng.

Hu ht cc tin cung cp thng tin nh kiu. Chng hn nh:

Type(subClassOf, Property): cho bit subClassOf l mt thuc tnh. Cc tn bin bt u bng du ?.

V t c bn (predicate)

PropVal(P, R, V ): mt v t vi 3 i s, dng biu din mt pht biu RDF vi ti nguyn R, thuc tnh P v gi tr V.

Type(R, T): vit tt ca PropVal(type, R, T), ch r ti nguyn R c kiu T Type(?r, ?t) PropVal(type, ?r, ?t)

Cc pht biu

Mt pht biu RDF (l mt b ba) (P, R, V) c biu din nh PropV al(P,R,V)

Lp (class)

Tt c cc lp l nhng thc th (instance) ca Class. Vi cc hng (constant): Class, Resource, Property, Literal., cc lp c kiu Class:

Type(Class,Class) Type(Resource,Class) Type(Property,Class) Type(Literal,Class)

Ti nguyn (resource) l lp ph bin nht. Mi i tng, mi lp v mi thuc tnh l nhng ti nguyn:

Type(?p, Property) Type(?p,Resource) Type(?c,Class) Type(?c,Resource)

V t trong pht biu RDF phi l mt thuc tnh:

PropVal(?p, ?r, ?v) Type(?p, Property)

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Thuc tnh type

type l mt thuc tnh:

Type(type, Property) Pht biu ny tng ng vi PropVal(type, type, Property).

Thuc tnh FuncProp

Thuc tnh hm l mt thuc tnh l mt hm. Thuc tnh FuncProp lin kt

mt ti nguyn vi ti a mt gi tr.

FuncProp hng (constant) biu din lp ca tt c cc thuc tnh hm. P l mt thuc tnh hm nu v ch nu n l mt thuc tnh, v khng c x, y1, v y2 sao cho

P(x, y1), P(x, y2), v y1 y2 Type(?p, FuncProp)

Type(?p, Property) ?r?v1?v2 PropVal(?p, ?r, ?v1) PropVal(?p, ?r, ?v2) ?v1 = ?v2

Cc pht biu c th ho (statements)

Pht biu constant biu din lp ca tt c cc pht biu c th ha. Tt c cc pht biu c th ha l cc ti nguyn, v pht biu l mt thc th (instance) ca Class:

Type(?s, Statement) Type(?s, Resource) Type(Statement, Class)

Mt pht biu c th ha c th c phn tch thnh 3 phn ca b ba RDF: Type(?st, Statement)

?p?r?v (PropVal(Predicate, ?st, ?p) PropVal(Subject, ?st, ?r) PropVal(Object, ?st, ?v))

Ch th (subject), v t (predicate) v i tng (object) l cc thuc tnh hm. Ni cch khc, mi pht biu c chnh xc 1 ch th, mt v t v 1 i tng:

Type(Subject, FuncProp) Type(Predicate, FuncProp) Type(Object, FuncProp)

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Thng tin nh kiu ca chng l:

PropVal(Subject, ?st, ?r) (Type(?st, Statement) Type(?r,Resource)) PropVal(Predicate, ?st, ?p) (Type(?st, Statement) Type(?p, Property)) PropVal(Object, ?st, ?v)

(Type(?st, Statement) (Type(?v,Resource) V Type(?v,Literal)))

Tin cui cng l nu i tng nh thuc tnh trong pht biu RDF, th n phi p dng cho mt pht biu c th ha v c nh gi tr hoc l mt ti nguyn hoc l mt literal.

Phn t container Tt c cc container l cc ti nguyn:

Type(?c,Container) Type(?c,Resource) Cc container l cc danh sch (list):

Type(?c,Container) list(?c) Cc container l cc bag hay cc sequence hay cc alternative:

Type(?c,Container) (Type(?c,Bag) V Type(?c, Seq) V Type(?c,Alt)) Cc bag v sequence l disjoint (tch bit):

(Type(?x,Bag) Type(?x, Seq)) i vi mi s t nhin n > 0, c mt b chn (selector), s chn phn t th n

ca mt container. l mt thuc tnh hm: Type(_n, FuncProp) v ch p dng cho cc container:

PropVal(_n, ?c, ?o) Type(?c,Container)

b. RDF Schema (Lc RDF)

b.1 Gii thiu

RDF l mt ngn ng ph bin, cho php ngi dng m t cc ti nguyn bng cch s dng b t vng ca chnh ngi dng. RDF khng to ra cc gi nh v bt k min ng dng c th no, cng khng nh ngha ng ngha ca bt k min no. RDF Schema s gip ngi dng lm c iu .

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XML Schema bt buc ti liu XML phi c cu trc, trong khi RDF Schema nh ngha t vng c dng trong m hnh d liu RDF. Trong RDFS, chng ta c th nh ngha t vng, ch r cc thuc tnh no p dng cho cc loi i tng no v gi tr no m chng c th nhn, ch r cc lp v m t cc mi quan h gia cc

i tng, gia cc lp.

b.2 Nhng khi nim c bn

Lp v thuc tnh

Mt lp c th c xem nh mt b cc phn t. Cc i tng ring l thuc v mt lp c tham chiu n nh cc thc th ca lp . S dng rdf:type nh ngha mi quan h gia cc thc th v cc lp trong RDF.

Trong cc ngn ng lp trnh, vic nh kiu c s dng ngn nga s v ngha (nonsense) c to ra. gii hn cc gi tr ca thuc tnh, ta gii hn range ca thuc tnh. gii hn cc i tng ca thuc tnh, ta gii hn domain ca thuc tnh.

Cc thuc tnh c nh ngha mt cch ring bit vi cc lp. Mi thuc tnh c m t bi rdfs:domain v rdfs:range, v n gii hn s kt hp cc thuc tnh vi cc lp. Mt thuc tnh c th c nh ngha c nhiu lp.

K tha v phn cp lp

Khi xc nh cc lp, chng ta cn phn loi, phn nhm cc lp theo cp bc thit lp cc mi quan h gia chng. Thng thng, A l mt lp con ca B nu mi

thc th (instance) ca A cng l mt thc th ca B.

Trong RDF Schema, cc lp khng nht thit phi lin kt vi nhau hnh thnh

nn mt phn cp nghim ngoc. Mt lp c th c nhiu lp cha (superclass). Nu lp A l mt lp con ca c B1 v B2, th mi thc th ca A l thc th ca c B1 v

B2.

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Hnh 2.3 S phn cp lp (Ngun t: A Semantic web Primer (2004), Grigoris Antoniou and Frank van Harmelen, page 82, figure 3.5)

Lp (class), s k tha (inheritance) v thuc tnh (property) tuy c nhng im tng ng, nhng cng c nhng im khc nhau. Trong lp trnh hng i tng,

mt lp i tng xc nh cc thuc tnh. thay i mt lp, ta thm cc thuc tnh

mi vo trong mt lp. Trong s phn cp lp, cc lp k tha cc thuc tnh ca t

tin.

C th nh ngha cc thuc tnh mi p dng cho mt lp c m khng lm thay i lp v cng c th s dng cc lp c nh ngha bi cc lp khc, sa chng li sao cho ph hp vi cc yu cu ca ngi dng thng qua cc thuc tnh mi.

Phn cp thuc tnh

Cc mi quan h phn cp gia cc lp c th c nh ngha. Chng hn nh

is taught by(c dy bi) l thuc tnh con ca involves (c quan h): nu mn hc C c dy bi ging vin A, th C cng c quan h vi A. S o ngc ca thuc tnh c th ng nhng i khi c th khng ng.

Thng thng, P l thuc tnh con ca Q nu Q (x, y) cha P (x, y).

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b.3 Ng ngha tin cho RDF Schema

to ng ngha tng minh v my c th s dng c (machine accessible), chng ta cn m t ng ngha ca RDFS ging nh logic. Do , cn c s h tr ca

cc b lp lun (reasoner) t ng x l cc cng thc logic. Gii thiu

Tt c cc t mu (primitives) trong RDF Schema c biu din thng qua cc hng (constant): Resource, Class, Property, subClassOf Mt vi v t c sn c s dng nh nn tng biu din cc mi quan h gia cc hng.

Hu ht cc tin cung cp thng tin nh kiu. Chng hn nh:

Type(subClassOf, Property): cho bit subClassOf l mt thuc tnh. Cc tn bin bt u bng du ?.

V t c bn (predicate)

PropVal(P, R, V): mt v t vi 3 i s, dng biu din mt pht biu RDF vi ti nguyn R, thuc tnh P v gi tr V.

Type(R, T): vit tt ca PropVal(type, R, T), ch r ti nguyn R c kiu T Type(?r, ?t) PropVal(type, ?r, ?t)

Lp con v thuc tnh con subClassOf l mt thuc tnh:

Type(subClassOf, Property) Nu C l mt lp con ca lp C, th tt c cc thc th (instance) ca C cng l

cc thc th ca C:

PropVal(subClassOf, ?c, ?c) (Type(?c,Class) Type(?c,Class) ?x(Type(?x, ?c) Type(?x, ?c)))

Tng t i vi subPropertyOf; P l mt thuc tnh con ca P nu P (x, y) cha P (x, y):

Type(subPropertyOf, Property) PropVal(subPropertyOf, ?p, ?p) (Type(?p, Property) Type(?p,Property) ?r?v(PropVal(?p, ?r, ?v) PropVal(?p, ?r, ?v)))

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Cc rng buc (constraints)

Mi ti nguyn rng buc l mt ti nguyn: PropVal(subClassOf,ConstraintResource,Resource)

Cc thuc tnh rng buc l tt c cc thuc tnh m cng l cc ti nguyn rng buc:

Type(?cp,ConstraintProperty) (Type(?cp,ConstraintResource) Type(?cp, Property))

Domain v range l cc thuc tnh rng buc:

Type(domain,ConstraintProperty) Type(range,ConstraintProperty)

Domain v range ln lt xc nh domain v range ca mt thuc tnh. Domain ca thuc tnh P l tp hp ca tt c cc i tng m P p dng vo. Nu domain ca P l D, th vi mi P (x, y), x D.

PropVal(domain, ?p, ?d) ?x?y(PropVal(?p, ?x, ?y) Type(?x, ?d)) Range ca thuc tnh P l tp hp ca tt c cc gi tr P c th nhn. Nu range

ca P l R, th vi mi P (x, y), y R.

PropVal(range, ?p, ?r) ?x?y(PropVal(?p, ?x, ?y) Type(?y, ?r)) Cc cng thc c th c suy ra t rng buc trn:

PropVal(domain, range, Property) PropVal(range, range,Class) PropVal(domain, domain, Property) PropVal(range, domain,Class)

c. S khc nhau gia RDF v RDFS

RDF thng dng m t cc thc th (instances) ca cc ontology, trong khi RDF Schema m ha cc ontology, s dng cc thnh phn Class, subClassOf, Property, subPropertyOf ch r cc lp, cc quan h gia cc lp, nh ngha cc thuc tnh v lin kt chng vi cc lp.

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Xem hnh 4: cc hnh khi vung l cc thuc tnh, cc hnh eclipse nm trn

ng gch ni nm ngang l cc lp, v cc hnh elip nm di ng gch ni nm ngang l cc thc th (instance).

Hnh 2.4 Cc lp RDF v RDFS (Ngun t: A Semantic web Primer (2004), Grigoris Antoniou and Frank van Harmelen, page 84, figure 3.6)

d. Ngn ng truy vn SPARQL [1] Khng ging OWL v RDF(S), SPARQL khng dnh cho ontology v s biu

din ti nguyn, nhng n dnh cho vic truy vn d liu web. N l ngn ng truy vn cho RDF. SPARQL c s dng :

Rt trch thng tin t lc RDF di dng URIs, bNodes v cc nguyn th (literals) c nh dng r rng.

Rt trch cc lc con ca RDF.

Xy dng cc lc RDF mi da trn cc thng tin trong cc biu c truy vn.

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Cc truy vn ca SPARQL ph hp vi (match) cc m hnh lc da trn lc ch ca truy vn. C m hnh ging nh cc lc RDF, nhng cha cc

bin c nh tn ti mt vi nt (ti nguyn) hoc cc lin kt/cc v t (thuc tnh). M hnh lc n gin nht ging nh b ba ca RDF (resource-property-value hoc O-A-V).

Hy xem 2 b ba RDF sau:

Hnh 2.5 Hai b ba RDF

(Ngun t: Dragan Gasevic, Dragan Djuric, Vladan Devedzic (2006), Model Driven Architecture and Ontology Development, fig.3.12, trang 93)

C hai b ba trn ph hp vi m hnh b ba sau:

Hnh 2.6 M hnh b ba (?album, music:author, ?author) ca RDF (Ngun t: Dragan Gasevic, Dragan Djuric, Vladan Devedzic (2006), Model Driven Architecture and Ontology

Development, fig.3.13, trang 93)

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Mt s ni kt l mt nh x t mt bin trong mt truy vn n cc thut ng. Mi b ba ca 2 b ba trn l mt gii php m hnh (mt tp cc ni kt ng) cho m hnh b ba. Cc kt qu truy vn trong SPARQL l tp cc gii php m hnh. Cc kt qu ca truy vn c biu din bi m hnh b ba l nhng gii php m hnh sau:

Cc m hnh lc n gin c th c kt hp thng qua vic s dng cc ton t khc nhau thnh cc m hnh lc phc tp hn. Chng hn nh, lc

RDF phc tp hn nh sau:

Hnh 2.7 Lc RDF phc tp (Ngun t: Dragan Gasevic, Dragan Djuric, Vladan Devedzic (2006), Model Driven Architecture and Ontology

Development, fig.3.14, trang 94)

tng hp (match) vi m hnh lc SPARQL phc tp hn sau:

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Hnh 2.8 Lc SPARQL phc tp (Ngun t: Dragan Gasevic, Dragan Djuric, Vladan Devedzic (2006), Model Driven Architecture and Ontology

Development, fig.3.14, trang 94)

V gii php m hnh s l:

V mt c php, cc truy vn SPARQL thuc mt trong nhng dng c biu din trong hnh sau:

R rng, c php rt ging c php ca cc ngn ng truy vn c s d liu nh SQL. Mnh SELECT cha cc bin (variables), bt u bng du ? hoc du $. Mnh WHERE cha mt m hnh (pattern). Cc Prefix c s dng nh mt c cu vit tt (abbreviation mechanism) cho cc URI v p dng cho ton b truy vn.

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e. Kt lun

RDF cung cp mt nn tng cho s biu din v x l siu d liu. RDF c m hnh d liu da trn biu , vi cc khi nim quan trng nh

resouce (ti nguyn), property (thuc tnh) v statement (pht biu). Mt pht biu (statement) l mt b ba ti nguyn-thuc tnh-gi tr.

RDF c cu trc da trn XML h tr kh nng tng tc c php. XML v RDF b sung cho nhau bi v RDF h tr thao tc c php.

RDF c s phn quyn v cho php xy dng tri thc thng d (incremental), ti s dng v chia s.

RDF l mt min (domain) c lp. RDF Schema cung cp k thut m t nhng min c th.

RDF Schema l ngn ng ontology nguyn thy. N cung cp cc t mu nn

tng v c cc khi nim quan trng nh lp (class), quan h ca lp con (subclass relation), thuc tnh (property), quan h ca thuc tnh con (subproperty relation), v gii hn domain v gii hn range.

RDF v RDFS cng c h tr bi cc ngn ng truy vn..

B. Ngn ng ontology web (OWL)

b.1 Gii thiu

RDF v RDF Schema cn nhiu hn ch trong vic din t: RDF b gii hn i vi cc v t nn tng nh phn, v RDF Schema b gii hn i vi s phn cp lp con (subclass hierarchy) v s phn cp thuc tnh (property hierarchy), cng vi cc nh ngha range v domain ca nhng thuc tnh ny.

V th, cn c mt ngn ng xy dng m hnh mnh hn khc phc nhng hn ch trn. V ngn ng OWL (Ontology web Language) ra i.

OWL k tha t DAML+OIL. Tn DAML+OIL l s kt hp gia tn DAML-

ONT (http://www.daml.org/2000/10/daml-ont.html) do M xut v ngn ng OIL (http://www.ontoknowledge.org/oil/) do Chu u xut.

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Ging nh DAML+OIL, b t vng OWL gm mt tp cc thuc tnh v phn t ca XML vi ng ngha c nh ngha r rng. OWL dng m t cc thut ng ca mt min v cc mi quan h gia cc thut ng trong mt ontology.

S hnh thnh OWL:

Hnh 2.9 S hnh thnh OWL (Ngun t: Dragan Gasevic, Dragan Djuric, Vladan Devedzic (2006), Model Driven Architecture and Ontology

Development, fig.3.14, trang 90)

b.2 Nhng yu cu ca ngn ng ontology

C php c nh ngha tng minh

C php phi r rng my c th x l thng tin. H tr lp lun hiu qu

Cho php kim tra cc trng hp nhm thit k cc ontology ln, tch

hp v chia s cc ontology t cc ngun khc

Mt ng ngha hnh thc

Ng ngha hnh thc m t chnh xc ng ngha ca tri thc. Ng ngha l iu

kin tin quyt cho h tr lp lun, n cho php:

Kim tra tnh nht qun ca ontology v tri thc

Kim tra cc mi quan h gia cc lp khng c nh trc

Phn cp t ng cc thc th trong cc lp

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kh nng din t

Thun li cho s din t

b.3 OWL

OWL l mt m rng ca RDF Schema. V ng ngha, OWL dng ng ngha ca cc lp v cc thuc tnh ca RDF (rdfs:Class, rdfs:subClassOf) v thm cc t vng nn tng vo h tr s din t phong ph hn. S m rng cng ph hp vi kin trc phn tng ca web ng ngha.

b.3.1 Ba loi OWL

OWL Full OWL Full s dng tt c cc t vng nn tng (primitive) ca ngn ng OWL.

N cho php kt hp ty cc t vng nn tng vi RDF v RDF Schema. iu ny c th lm thay i ng ngha ca cc t vng nn tng (RDF hoc OWL) c nh trc bng cch p dng cc t vng ngn ng (language primitive) vo vi nhau.

u im ca OWL Full: hon ton tng thch t di ln (upward-compatible) vi RDF c v c php ln ng ngha: mi ti liu RDF no hp l th cng l ti liu

OWL Full hp l, v mi kt lun ca RDF/RDF Schema no c gi tr (valid) th cng l kt lun ca OWL c gi tr (valid).

Nhc im ca OWL Full: ngn ng tr nn qu mnh m n mc l khng th quyt nh c (undecidable), nh hng n h tr lp lun y hoc h tr lp lun hiu qu.

OWL DL

OWL DL l mt ngn ng con ca OWL Full, c th s dng cc hm to lp (constructor) t OWL, cung cp s din t ti u v m bo tt c cc kt lun l c th d tnh c v s hon thnh trong mt thi gian nht nh.

u im ca OWL DL: cho php h tr lp lun hiu qu.

Nhc im: mt ton b tnh tng thch vi RDF. Thng thng, mt ti liu RDF phi c m rng theo mt s cch v b gii hn theo cc cch khc trc khi n l mt ti liu OWL DL hp l. Mi ti liu OWL DL hp l l ti liu RDF hp l.

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OWL Lite

Dng cho vic xy dng cc phn cp nhm v cc rng buc n gin. Nhc im ca OWL Lite: loi b cc lp c lit k, cc pht biu tch bit

(disjointness) v gi tr cardinality (s ca gi tr) ch c php l 0 v 1. Rt hn ch trong s din t.

u im ca OWL Lite: d s dng v d thc thi

b.3.2 S la chn ngn ng con

Vic la chn ngn ng con no ph hp nht l ph thuc vo nhu cu ca mi

ngi. S la chn gia OWL Lite v OWL DL ph thuc vo phm vi ngi dng cn cu trc din t. S la chn gia OWL DL v OWL Full ch yu ph thuc vo phm vi ngi dng cn nhng tin ch xy dng siu m hnh (metamodeling) ca RDF Schema.

b.3.3 Tnh tng thch ca ba ngn ng con

Mi ontology OWL Lite hp l th cng hp l trn ontology OWL DL

Mi ontology OWL DL hp l th cng hp l trn ontology OWL Full

Mi kt lun ca OWL Lite c gi tr th cng c kt lun c gi tr trn

OWL DL

Mi kt lun ca OWL DL c gi tr th cng c kt lun c gi tr trn OWL Full

b.3.4 Mi quan h gia OWL v RDF/RDFS

Tt c cc loi OWL u dng RDF cho c php ca chng Cc thc th (instance) c khai bo ging nh trong RDF, s dng

cc m t ca RDF v thng tin nh kiu

Cc hm to lp (constructor) ca OWL, chng hn nh owl:Class v owl:DatatypeProperty v owl:ObjectProperty l nhng c trng ca cc bn sao (counterpart) ca OWL

Hnh 5 biu th cc mi quan h ca lp con gia mt vi t vng mu nn tng ca OWL v RDF/RDFS

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Hnh 2.10 Mi quan h ca lp con gia OWL v RDF/RDFS (Ngun t: A Semantic web Primer (2004), Grigoris Antoniou and Frank van Harmelen, page 115, figure 4.1)

b.3.5 Ngn ng OWL

C php

OWL xy dng da trn RDF v RDF Schema v s dng c php da trn XML ca RDF:

C php da trn XML (http://www.w3.org/TR/owl-xmlsyntax/) khng tun theo cc quy c ca RDF.

C php tru tng c s dng trong ti liu nh kiu ngn ng (http://www.w3.org/TR/owl-semantics/) th sc tch v d c hn nhiu so vi hoc l c php XML hoc l c php RDF/XML.

C php lc da trn cc quy c ca UML (Unified Modeling Language_Ngn ng xy dng m hnh hp nht) c s dng rng ri, v gip con ngi tr nn quen thuc vi OWL.

Tiu (header)

Ti liu OWL thng c gi l ontology OWL. Phn t gc ca ontology

OWL l phn t rdf:RDF, v cng cho bit s lng khng gian tn (namespace):

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Ontology OWL c th bt u vi mt b xc nhn (assertions). Nhng xc nhn ny c nhm li di phn t owl:Ontology, v cha cc ch thch (comments), s kim tra phin bn v k c cc ontology khc. V d:

An example OWL ontology University Ontology

owl:imports lit k cc ontology khc m ni dung ca n l mt phn ca ontology hin ti. Cc namespace c s dng hp nht, cn cc ontology c nhp vo cung cp cc nh ngha s dng. Thng c mt phn t import cho mi namespace c s dng, nhng cng c th nhp thm cc ontology khc.

Ngoi ra, owl:imports cn l thuc tnh bc cu: nu ontology A nhp vo ontology B, v ontology B nhp vo ontology C, th ontology A cng nhp vo

ontology C.

Phn t lp (class elements)

Cc lp c nh ngha bng cch s dng phn t owl:Class (lp con ca rdfs:Class). Chng hn, chng ta nh ngha lp associateProfessor nh sau:

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Lp ny l tch bit (disjoint) vi lp assistantProfessor v professor khi dng phn t owl:disjointWith. Nhng phn t ny c th nm trong nh ngha trc, hoc c thm vo bng cch tham chiu n ID thng qua vic s dng rdf : about. C ch ny c k tha t RDF.

Tnh tng ng (equivalence) ca cc lp c th c nh ngha bng cch s dng phn t equivalentClass:

C 2 lp c nh ngha trc: owl:Thing (cha mi th) v owl:Nothing (lp rng). Mi lp l mt lp con ca owl:Thing v mt lp cha (superclass) ca owl:Nothing.

Phn t thuc tnh

Thuc tnh i tng: lin kt i tng vi i tng. V d nh isTaughtBy v supervises

Thuc tnh kiu d liu: lin kt i tng vi gi tr kiu d liu. V d nh phone, title, age

OWL khng yu cu nh ngha trc kiu d liu v cng khng cung cp cc tin ch nh ngha c th.

V d v thuc tnh kiu d liu:

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Cc kiu d liu do ngi dng nh ngha thng c tp hp trong XML Schema v sau c s dng trong ontology OWL.

V d v thuc tnh i tng:

OWL cho php lin kt cc thuc tnh o (inverse properties). V d nh cp

isTaughtBy v teaches:

Hnh 6 minh ha mi quan h gia mt thuc tnh v s o ngc ca thuc

tnh .

Hnh 2.11 Cc thuc tnh o (Ngun t: A Semantic web Primer (2004), Grigoris Antoniou and Frank van Harmelen, page ?, figure 4.2)

Tnh tng ng (equivalence) ca cc thuc tnh c th c nh ngha thng qua vic s dng phn t owl:equivalentProperty.

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Gii hn thuc tnh

Vi rdfs:subClassOf, chng ta c th ch r lp C l lp con ca lp C khc. Khi , mi thc th (instance) ca C cng l thc th ca C.

Phn t sau yu cu cc mn hc nm u tin (first-year courses) ch c dy bi gio s (professor):

owl:allValuesFrom ch r lp ca cc gi tr m thuc tnh c ch r bi owl:onProperty c th nhn. Ni cch khc, tt c cc gi tr ca thuc tnh phi n

t lp ny. Trong v d trn, ch c cc gio s (professor) c cho php nh cc gi tr ca thuc tnh isTaughtBy.

C th khai bo mn ton (mathematics courses) c dy bi David Billington nh sau:

owl:hasValue ch ra gi tr c th m thuc tnh c ch r bi owl:onProperty.

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Thng thng, phn t owl:Restriction gm mt phn t owl:onProperty v

t nht mt khai bo gii hn. Mt kiu khai bo gii hn khc xc nh cc gii hn cardinality. Chng hn

nh, chng ta mun mi mn hc (course) c dy bi t nht mt ai :

1

1 l literal, c hiu nh nonNegativeInteger. S dng khai bo khng gian tn (namespace) xsd phn t header tham chiu n ti liu XML Schema.

Nh vy, owl:Restriction xc nh lp n khng c ID, khng c nh ngha

bi owl:Class, v ch c phm vi cc b (ch s dng ti mt ni m s gii hn xut hin). Khi ni n cc lp, l ni n 2 ngha: th nht, lp m c nh ngha bi owl:Class vi mt ID, v lp n cc b (i tng tha mn cc iu kin gii hn no hoc kt hp vi cc lp khc). Th hai, thng c gi l s din t ca lp.

Cc thuc tnh c bit

Mt vi thuc tnh ca cc phn t thuc tnh c th c nh ngha trc tip:

owl:TransitiveProperty: xc nh thuc tnh bt cu (transitive property), nh l has better grade than, is taller than hoc is ancestor of.

owl:SymmetricProperty: xc nh thuc tnh i xng (symmetric property), nh l has same grade as hoc is sibling of.

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owl:FunctionalProperty: xc nh thuc tnh c nhiu nht 1 gi tr

cho mi i tng, nh l age, height hoc directSupervisor. owl:InverseFunctionalProperty: xc nh thuc tnh cho 2 i tng

khc nhau no khng c cng gi tr, chng hn nh thuc tnh

isTheSocialSecurityNumberfor.

Kt hp kiu Boolean Chng ta c th kt hp cc kiu Boolean (union_hp, intersection_giao,

complement_b sung) ca cc lp li vi nhau. V d: chng ta c th ni rng cc mn hc (course) v cc thnh vin nhn vin

(staff members) l tch bit (disjoint) nh sau:

Nh vy, mi course l mt thc th (instance) ca complement ca staff member, tc l khng c course no l staff member. Tuy nhin, pht biu ny cng c th c din t bng cch s dng owl:disjointWith.

S hp (union) ca cc lp c xy dng bng cch s dng owl:unionOf:

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S giao (intersection) c pht biu bng owl:intersectionOf:

Chng ta xy dng im giao nhau ca 2 lp, mt trong s c n: lp ca tt c cc i tng thuc v SCDepartment. Lp ny giao vi faculty cho bit ton b cn b ging dy ca mt khoa (faculty) trong CSDepartment.

Cc kt hp kiu Boolean c th c lng vo nhau mt cch ty :

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S lit k

Mt lit k l mt phn t owl:oneOf, c s dng nh ngha mt lp bng cch lit k tt c cc phn t ca n:

Cc thc th (instances)

Cc thc th (instance) ca cc lp c khai bo ging nh trong RDF:

Hoc

Chng ta c th vit chi tit hn nh sau:

39

OWL khng chp nhn unique-names assumption (gi nh tn duy nht) bi v 2 thc th c tn khc nhau hoc ID khng r rng l 2 c th (individuals) khc nhau.

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OWL cung cp mt ch thch ngn (shorthand notation) xc nhn s khc nhau tng cp ca tt c cc c th trong bng lit k c sn:

owl:distinctMembers ch c th c s dng trong s kt hp vi owl:allDifferent.

Cc kiu d liu (data types)

Khng phi tt c cc kiu d liu XML Schema u c th c s dng trong OWL. Ti liu tham kho OWL (OWL reference document) lit k tt c cc kiu d liu XML Schema c th s dng, bao gm kiu chui (string), kiu s nguyn (integer), kiu lun l (boolean), kiu thi gian (time) v kiu ngy (date).

Thng tin xc nh phin bn

Pht biu owl:priorVersion ch r phin bn trc ca ontology hin ti. Thng tin ny khng c ng ngha l thuyt m hnh hnh thc, nhng c th c cc chng trnh v ngi c khai thc cho nhng mc ch qun l ontology.

Ngoi owl:priorVersion ra, OWL cn c 3 pht biu khc ch r thng tin xc nh phin bn:

owl:versionInfo: thng cha mt chui mang thng tin phin bn hin ti, chng hn nh t kha RCS/CVS.

owl:backwardCompatibleWith: cha mt tham chiu n ontology khc, nhn bit ontology c ch nh l phin bn trc ca ontology cha ng. Tt c cc trnh nh danh (identifier) t phin bn trc c cng cch hiu trong phin bn mi. V vy, n cp nht cc khai bo

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khng gian tn (namespace) v cc pht biu owl:imports tham chiu n URL ca phin bn mi.

owl:incompatibleWith: cho bit ontology cha ng l phin bn sau ca ontology c tham chiu. V c bn, iu ny l thuc quyn ca tc gi to ontology.

b.3.6 OWL trong OWL

Khng gian tn (namespaces)

]>

URI ca ti liu trn c nh ngha nh l namespace mc nh. Hn na, vic

s dng cc nh ngha thc th (entity) cho php chng ta vit tt URL trong cc gi tr thuc tnh.

Lp ca lp (Metaclasses)

Lp ca tt c cc lp chnh l lp con ca lp ca tt c cc lp ca RDF

Schema:

Class The class of all OWL classes

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Thing l lp i tng ph bin nht trong OWL, v Nothing l lp i tng rng.

Tnh tng ng ca lp

Tnh tng ng ca lp c biu th l owl:EquivalentClass, cho bit mi quan h ca lp con v lun lun c nh r gia 2 lp. iu ny l tng t nh

owl:EquivalentProperty. Cc pht biu disjointness ch c nh r gia cc lp.

EquivalentClass

EquivalentProperty

disjointWith

Tnh tng ng (equality) v tnh khng tng ng (inequality) ch c th c nh r gia nhng th ty . Trong OWL Full, pht biu ny cng c th c p dng cho cc lp. owl:sameAs hon ton ng ngha nh owl:sameIndividualAs.

sameIndividualAs

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differentFrom

sameAs

owl:distinctMembers ch c dng cho owl:AllDifferent:

AllDifferent distinctMembers

Xy dng lp t lp khc

owl:unionOf xy dng mt lp t danh sch.

unionOf

Tng t vi owl:intersectionOf v owl:oneOf.

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Gii hn thuc tnh ca cc lp

Cc gii hn trong OWL xc nh lp ca cc i tng tha mn mt vi

iu kin km theo:

Restriction

Tt c cc thuc tnh sau ch c php xut hin bn trong mt nh ngha gii hn (restriction definition), tc l domain ca chng l owl:Restriction, nhng chng khng tun theo range ca chng:

onProperty

allValuesFrom

hasValue

minCardinality

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Cc thuc tnh

owl:ObjectProperty l trng hp c bit ca rdf:Property.

ObjectProperty

Tng t i vi owl:DatatypeProperty. V owl:TransitiveProperty ch p

dng cho cc thuc tnh i tng:

TransitiveProperty

V tng t i vi cc thuc tnh hm o, thuc tnh hm, thuc tnh i

xng.

b.4 Kt lun

OWL l mt chun dng cho ontology web, m t ng ngha ca tri thc theo cch m my c th s dng c.

OWL da trn RDF v RDFS. Cc thc th (instance) c nh ngha thng qua vic s dng m t RDF; v hu ht t vng mu (primitive) ca RDFS c s dng.

Ng ngha hnh thc v lp lun hnh thc c cung cp thng qua

vic nh x OWL vo logic. Logic v t v logic m t c s dng cho mc ch ny.

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2.2.1.3 Logic v suy din [2]

A. Gii thiu

S biu din tri thc xut hin trong lnh vc tr tu nhn to, trong trit hc v thm ch c t thi Hy lp c i; v Arictotle c xem l cha ca logic.

Logic vn cn l nn tng ca biu din tri thc, c bit l trong logic v t (logic bc nht). Logic rt ph bin v n cung cp mt ngn ng bc cao m tri thc c din t theo cch d hiu v c kh nng din t cao. N c ng ngha hnh thc d hiu, v nh r ng ngha tng minh ca cc pht biu logic. Nh vy, logic c th cung cp cc gii thch cho cc cu tr li.

Cc ngn ng RDF v OWL (Lite v DL) c xem nh l cc c th ha ca logic v t. S ph hp c minh ha bng cc ng ngha tin di dng cc tin logic. Mc khc, cc lut khng th xc nhn thng tin m mt ngi hoc l n

ng (man) hoc l n b (woman), trong khi thng tin ny c din t d dng trong OWL bng cch s dng union disjoint.

Tuy nhin, tin ca lut c th khng nm trong kh nng din t ca logic v t nn cn c mt kiu h thng lut mi. H thng lut ra i ph thuc vo lng

thng tin nhn c (y hay khng y ).

B. Cc lut n iu

b.1 V d

Gi s ta c cc v t c bn v mi quan h gia nh sau:

mother(X,Y ) X is the mother of Y father(X,Y ) X is the father of Y male(X) X is male female(X) X is female

T cc v t ny, chng ta c th nh ngha cc mi quan h xa hn nh s dng cc lut thch hp:

nh ngha mt parent (ba m): mt parent l hoc father (cha) hoc m (mother):

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mother(X,Y ) parent(X,Y ) father(X,Y ) parent(X,Y )

nh ngha mt brother: (anh em trai) l ngi n ng c chung parent:

male(X), parent(P,X),parent(P,Y ),notSame(X,Y ) brother(X,Y )

V t notSame ch r s khc nhau

sister (ch em gi): l ngi n b c chung parent:

female(X), parent(P,X), parent(P,Y ), notSame(X,Y ) sister(X,Y )

Uncle (cu): l brother (anh em trai) ca parent (ba m):

brother(X,P), parent(P,Y ) uncle(X,Y )

Grandmother (b): l mother (m) ca parent (ba m):

mother(X,P), parent(P,Y ) grandmother(X,Y )

Ancestor (ng b t tin) hoc l parent (ba m) hoc l ancestor (t tin) ca parent:

parent(X,Y ) ancestor(X,Y ) ancestor(X,P), parent(P,Y ) ancestor(X,Y )

b.2 C php ca lut n iu

Xt mt lut n gin: tt c cc khch hng thng xuyn trn 60 tui c hng quyn gim gi c bit:

loyalCustomer(X), age(X) > 60 discount(X)

Cc thnh phn ca lut:

variables (bin): X constants (hng): l cc gi tr c nh: 60 predicates (v t): lin kt cc i tng: loyalCustomer, > function symbols (k hiu hm): tr li gi tr cho nhng i s no : age

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b.2.1 Lut

Mt lut r c dng (k hiu l pl(r)): B1,...,Bn A

y, A, B1,,Bn l cc cng thc nguyn t. A l head ca lut, v B1,,Bn l cc tin ca lut. Tp {B1,,Bn} c tham chiu n body ca lut.

Du , trong body ca lut c c ni tip nhau: nu B1 v B2 v v Bn ng, th A cng ng.

Thng thng, tt cc cc bin xut hin trong mt lut u c tnh n, tnh ph

qut v tnh nh lng (dng X)

V vy, c th biu din lut r trn nh sau:

X1 ... Xk((B1 ... Bn) A)

Hoc l:

X1 ... Xk (A B1 ... Bn) y X1,,Xk l tt c cc bin xut hin trong A, B1,,Bn

b.2.2 Cc s kin (facts)

S kin l cng thc nguyn t. V d: loyalCustomer(a345678), cho bit khch hng c ID a345678 l khch hng thng xuyn. Cc bin ca s kin c tnh n, tnh ph qut v tnh nh lng.

b.2.3 Cc chng trnh logic

Chng trnh logic P l mt tp cc s kin v cc lut c ngi. S tnh tuyn

ca logic v t pl(P) l tp tt c cc biu din ca cc lut v cc s kin ca logic v t trong P.

b.2.4 Cc mc tiu (goals)

Mt goal c dng:

B1,...,Bn

Nu n=0, chng ta c goal r ng:

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Cc goal trong logic v t c biu din nh sau:

X1 ... Xk (B1 ... Bn)

Hoc l:

X1 ...Xk(B1 ... Bn)

y, X1,,Xk l tt c cc bin xut hin trong B1,,Bn.

b.3 Ng ngha ca lut n iu

tr li mt truy vn ta dng suy din ca logic v t ca cc lut, cc s kin v cc cu hi. Gi s cho trc mt chng trnh logic P v mt truy vn:

B1,..., Bn

Vi cc bin X1,,Xk, chng ta tr li chc chn khi no v ch khi no:

pl(P) |= X1 ... Xk(B1 ... Bn) (1) Hoc tng ng khi no:

pl(P) {X1 ...Xk(B1 ... Bn)} l khng tha mn (2)

Chng ta a ra mt cu tr li chn chn nu s suy din ca logic v t ca chng trnh P, cng vi s suy din ca truy vn ca logic v t l khng tha mn.

Cc lng t ,,,, , c ngha ln lt l not (khng), or (hoc), and (v), implies (hm ), for all (vi mi), there is (tn ti).

(1) v (2) cho bit: khi s suy din ca logic v t P l ng, th X1 ... Xk(B1 ...Bn) cng phi ng. Tc l, c tn ti cc gi tr cho cc bin X1,,Xk cho tt c cc cng thc nguyn t tr nn ng.

C. Lut khng n iu

c.1 Gii thiu

Trong cc h thng lut khng n iu, mt lut khng c p dng cho tt c cc tin bi v chng ta cn phi xt ti cc chui lp lun i lp. Thng chng ta xt cc lut defeasible bi v chng s b cc lut khc hy b. chp nhn cc

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xung t gia cc lut, cc cng thc nguyn t ph nh c th xut hin trong

head v body ca cc lut. Chng hn nh, chng ta c th vit:

p(X) q(X) r(X) q(X)

phn bit gia cc lut defeasible, lut standard v lut n iu, chng ta dng mt mi tn nh sau:

p(X) q(X) r(X) q(X)

C th gii quyt s xung t bng cch s dng quyn u tin: mt lut no c u tin th lut s c chp nhn. Cc quyn u tin c s dng da trn nhng nguyn tc: tnh tin cy, tnh mi v tnh c th ca lut. Tuy nhin, quan

h quyn u tin khng c tnh chu k (acyclic), ngha l khng th c s lp li ca hnh thc: r1 >r2 > ...>rn >r1

c.2 nh ngha c php

Mt lut defeasible c dng:

r : L1,...,Ln => L

y, r l nhn, {L1 ,...,Ln} l body (hoc cc tin ), v L l head ca lut. L,L1,...,Ln l cc literal khng nh hoc literal ph nh (mt lieral l mt cng thc nguyn t p(t1,.,tn) hoc ph nh ca n p(t1,...,tn)). i khi chng ta ch r head ca mt lut l head(r), body ca n l body(r) v s dng nhn r tham chiu n tt c cc lut.

Mt chng trnh logic defeasible l mt b ba (F, R, >) bao gm mt tp F cc s kin, mt tp R c ngi ca cc lut defeasible, v mt quan h nh phn khng chu k > trn R.

D. Biu din cc lut n iu trong XML

Mc ch l to ra tri thc di dng cc lut m my c th s dng c.

d.1 Cc thut ng

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Cc thut ng (terms) c biu din bng cch dng cc th , , v . Chng hn nh thut ng sau:

f(X, a, g(b, Y)) c biu din nh sau:

f

X

a

g

b

Y

d.2 Cc cng thc nguyn t

i vi cc cng thc nguyn t, chng ta s dng thm th v th . Chng hn nh, cng thc:

p(X, a, f(b, Y))

c biu din nh sau:

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p

X

a

f

b

Y

d.3 Cc s kin (facts)

Mt s kin ch l mt cng thc nguyn t, c bao bc bi cc th ng v m. Chng hn nh, s kin p(a) c biu din nh sau:

p

a

d.4 Cc lut

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Mt lut gm c mt head v mt body. head l mt cng thc nguyn t v body c th l mt s phi hp ca cc cng thc nguyn t (body c th l mt chui rng). Chng ta s dng cc th , v . Chng hn nh lut:

p(X, a),q(Y, b) r(X,Y )

c biu din nh sau:

r

X

Y

p

X

a

q

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Y

b

d.5 Cc truy vn

Cc truy vn c biu din nh cc body ca cc lut, c bao bc bi cc th .

E. Biu din cc lut khng n iu trong trong XML

So vi cc lut n iu, cc lut khng n iu c nhng khc nhau v mt c

php sau:

Khng c cc k hiu hm Cc nguyn t ph nh c th xut hin trong head v body ca lut Mi lut c mt nhn (label) Ngoi cc lut v cc s kin (facts), mt chng trnh cng cha cc

pht biu ca quyn u tin

F. Kt lun

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Cc lut khng n iu rt c ch trong cc tnh hung m thng

tin c hiu lc nhng khng y . Chng l nhng lut c th b cc lut khc loi b.

Cc quyn u tin c s dng gii quyt cc xung t gia cc lut khng n iu.

S biu din ca cc lut trong cc ngn ng nh ngn ng XML l khng phc tp.

2.2.1.4 Logic m t [1][6]

A. Gii thiu

Logic m t thuc h hnh thc biu din tri thc, biu din tri thc ca mt min ng dng bng cch, u tin, nh ngha cc khi nim lin quan ca min (thut ng), sau dng nhng khi nim ny ch r cc thuc tnh ca cc i tng v cc c th xut hin trong min . Logic m t c trang b thm ng ngha da trn logic v hnh thc, c bit l c h tr lp lun cho php suy din tri thc mt cch r rng t mt tri thc no .

S hp nht gia tnh din t ca logic m t v tnh phc tp ca nhng vn lp lun l mt trong nhng vn quan trng nht trong nghin cu logic m t. Tuy

nhin, s pht trin ca logic m t da trn cc tng xy dng c php c bn l cc khi nim nguyn t (cc v t nht nguyn), cc lut nguyn t (cc v t nh phn) v cc c th nguyn t (cc hng), kh nng din t ca ngn ng xy dng cc khi nim v cc lut phc tp, v s h tr ca trnh suy din.

H logic m t khng ch cha cc b thut ng (TBox) v cc b xc nhn (ABox) m cn gip cc dch v lp lun chng. Nhim v lp lun thut ng l xc nh liu mt m t c tha mn (khng c mu thun) hay khng? Hoc liu m t ny c tng qut hn m t kia hay khng? Tc l liu m t ny c xp gp vo m

t kia hay khng?

B. C php v ng ngha ca logic m t

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b.1 Quy tc k hiu Cc khi nim nguyn t k hiu l cc ch C, D Cc lut k hiu l cc ch R, S Cc lut hm (c im_features, thuc tnh_attributes) k hiu l cc ch f, g Cc s nguyn khng m (trong gii hn s) k hiu l n, m Cc c th (individuals) k hiu l a, b Trong tt c cc trng hp, chng ta c th dng ch s di dng (subscripts)

(thng dng khi nh ngha c php, ng ngha v trong cc v d tru tng).

Trong cc v d c th, cc quy tc sau thng dng: Tn khi nim bt u bng mt ch ci hoa, theo sau l nhng ch ci

thng (v d nh Human, Male). Tn lut (cng nh cc tn hm) bt u bng ch ci thng (v d nh

hasChild, marriedTo). Tn c th l ton ch ci hoa (v d nh CHARLES, MARY).

b.2 Cc m t khi nim v m t lut

Cc m t s cp l cc khi nim nguyn t (tn khi nim) v cc lut nguyn t (tn lut). Nhng m t phc tp c xy dng t cc m t s cp cng vi cc constructor khi nim v constructor lut.

Cc m t khi nim trong AL (Attributive Language) c hnh thnh theo lut c php sau:

(Syntax) (constructors) C, D A Khi nim nguyn t

T Khi nim tng qut Khi nim bottom

A Ph nh nguyn t C D Giao nhau (intersection) R.C Gii hn gi tr (value restriction)

R.T Lng t tn ti gii hn (limited existential quantification)

Trong AL, ph nh ch c p dng cho cc khi nim nguyn t, v ch c khi nim mc nh (top) c p dng cho phm vi s lng tn ti theo mt lut.

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Gi s Person v Female l nhng khi nim nguyn t, th Person Female v

Person Female l nhng khi nim ca AL ln lt m t nhng ngi l n b v nhng ngi khng phi n b. Ngoi ra, nu gi s hasChild l mt lut nguyn

t th chng ta c th to ra nhng khi nim Person hasChild.T v Person hasChild.Female cho bit nhng ngi c con ni chung, v nhng ngi c ton con gi. Ta c th s dng khi nim mc di (bottom) m t nhng ngi khng c con bng khi nim Person hasChild.

nh ngha ng ngha hnh thc ca cc khi nim AL, chng ta xem bin dch I gm mt tp hp khng rng I (min ca bin dch) v mt hm bin dch, gn cho mi khi nim nguyn t A mt tp AI I v gn cho mi lut nguyn t R mt quan h nh phn RI IxI. Hm bin dch c m rng cho cc m t khi nim bng nhng nh ngha quy np sau:

T =

= (A) = \ A

(C D) = C D (R.C) = {b.(a,b)R bC} (R.T) = {b.(a,b)R}

Hai khi nim C, D tng ng nhau (C D) nu C= Dcho tt c bin dch I. V d, hai khi nim hasChild.Female hasChild.Student v hasChild.(Female Student) l tng ng nhau.

b.3 Gii hn cho cc bin dch lut: Nhng gii hn ny yu cu cc bin dch lut phi tha cc thuc tnh no ,

nh l tnh bc cu (transitivity) v tnh hm (functionality). Nhng thuc tnh khc c th i xng (symmetry) hoc lin kt (connections) gia cc lut khc nhau.

b.3.1 Cc lut hm

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Xt mt tp con NF ca tp tn lut NR, th cc phn t ca n c gi l cc c tnh (features). Mt bin dch phi nh x cc features f n cc quan h nh phn hm fI I x I, ngha l cc quan h tha a,b,c.fI(a,b) fI(a,c) b = c. i khi cc quan h hm c xem nh hm khng y . V vy, ta vit fI(a) = b hn l vit fI(a,b). AL s dng thm cc feature c k hiu l ALf.

b.3.2 Cc lut bc cu

Xt mt tp con NR+ ca NR, th cc tn lut R NR+ c gi l cc lut bc cu. Mt bin dch phi nh x cc lut bc cu R NR+ vo cc quan h nh phn bc cu RI I x I. AL s dng thm cc lut bc cu c k hiu l ALR+.

b.3.3 Cc hm to lp (constructor) khi nim

Cc constructor khi nim a ra cc m t lut, m t khi nim, v chuyn chng thnh cc m t khi nim phc tp hn.

C php v ng ngha ca cc constructor khi nim thng dng ca logic m t:

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Bng 2.1 C php v ng ngha ca cc hm to lp (constructor) thng dng (Franz Baader, Deborah L. McGuinness, Daniele Nardi, Peter F. Patel-Schneider (), THE DESCRIPTION LOGIC

HANDBOOK: Theory, implementation, and applications, page 497)

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Mt vi c php tng minh ca cc constructor khi nim v chuyn chng

sang c php tru tng:

Bng 2.2 C php tng minh v tru tng ca cc constructor khi nim

(Franz Baader, Deborah L. McGuinness, Daniele Nardi, Peter F. Patel-Schneider (), THE DESCRIPTION LOGIC HANDBOOK: Theory, implementation, and applications, page 498)

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b.3.4 Cc contructor lut

Cc constructor lut a ra cc m t lut, m t khi nim, v chuyn chng

thnh cc m t lut phc tp hn. C php v ng ngha ca cc constructor lut

thng dng:

Bng 2.3 C php v ng ngha ca cc constructor lut thng dng (Franz Baader, Deborah L. McGuinness, Daniele Nardi, Peter F. Patel-Schneider (), THE DESC