Lập trình hướng Agent

LI GII THIUTrong nhng nm gn y, s pht trin mnh m ca cc cng ngh truyn thng v internet nh hng su rng n mi mt ca cuc sng t kinh t, khoa hc n vn ho v x hi. R rng s pht trin ca phn cng ng vai tr rt quan trng trong qu trnh tin ho ny nhng yu t then cht nh hng mnh m n x hi tri thc ngy nay chnh l bn thn phn mm. Khi m mng my tnh v Internet tr thnh ph bin th vic x l thng tin phn tn, chia x v tch hp thng tin thng qua ng truyn gia cc my vi nhng c s d liu c nhng khun dng khc nhau cng ngy cng tr nn ph bin. iu ny dn n mt thch thc mi i vi gii pht trin phn mm khi phi i u vi nhng yu cu thc t ca cc h phn mm phc tp, m v phn tn. Nhng nghin cu v cng nghip pht trin phn mm trong nhng cui nm 80 v u thp nin 90 xoay quanh cch tip cn hng i tng tin ho t phng php lun phn mm cu trc truyn thng. Phng php hng i tng c u im so vi phng php cu trc l kh nng s dng li m ngun, d c m ngun v x l li. tng c bn ca n l xem h phn mm nh tp hp cc thc th tng tc gi l i tng trong mi i tng c xc nh bi ba yu t: nh danh, trng thi v hnh vi1. Nh vy, pht trin phn mm da trn cch tip cn ny c ngha l tin hnh xy dng m hnh ca h thng cn c pht trin (c trong cc pha phn tch v thit k) da trn khi nim i tng v nhng khi nim lin quan nh thnh vin, phng thc, quan h... Ngn ng UML c s dng rng ri m hnh cc h phn mm ny di dng use case, biu lp, biu tng tc... Tuy nhin, cch tip cn hng i tng t ra khng p ng c nhu cu pht trin cc h phn mm m, phn tn, phc tp nh qun l mng vin thng, thng mi in t, tr gip vn phng, tm kim/lc thng tin...L mt pht trin tip theo ca hng i tng, cch tip cn hng agent c xem l cng ngh ha hn cho pht trin cc h phn mm phc tp ny. tng c bn ca h a agent l xem h phn mm nh mt cu trc x hi bao gm cc agent c kh nng t ch cng vi cc tng tc c tnh cht tri thc hay mang ng ngha gia chng. Ging nh i tng, cc agent cng c nh danh, trng thi v hnh vi nhng nhng khi nim ny c m t mt cch tinh t hn:

Trng thi c th bao gm tri thc, lng tin, ch cn phi tho mn, cc trchnhim c gn cho tng agent;1

Trng thi c m t bi b gi tr ca cc bin, hnh vi c m t theo cc phng thc c th c thc hin t trong chnh i tng hay gi t nhng i tng khc. Tng tc gia cc i tng c m t theo mt s cc quan h khc nhau c c gia chng.

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Hnh vi l nhng vai tr m agent c th m nhim, nhng cng vic cn phitin hnh, cc s kin cn phi c quan st... Cng ngh phn mm hng agent thu ht nhiu quan tm nghin cu v n c xem l cch tip cn tin ho t cng ngh phn mm hng i tng v cng ngh tri thc. N t ra c nhiu ha hn cho pht trin cc h phn mm trong mi trng phn tn v m. Thp nin 90 chng kin s n r ca nhiu ng dng v th nghim thnh cng trong cc lnh vc khc nhau nh vin thng, qun l khng lu, cc dch v trn Internet...Nhng nm 2000, cc nghin cu v agent tp trung vo xy dng cc phng php lun pht trin phn mm bao gm xy dng quy trnh, cng c cng cc k thut phn tch v thit k h a agent. Nh vy, cng ngh agent c nghin cu v pht trin mnh m trn th gii v c p dng trong nhiu lnh vc khc nhau. Tuy nhin, nhng nghin cu trong nc v agent mi ch giai on bt u v theo hiu bit ca chng ti nghin cu v cng ngh phn mm hng agent cha c quan tm nhiu. Nhm p ng nhu cu nghin cu v pht trin cc h phn mm a agent, ti tp trung xem xt quy trnh pht trin v cc k thut cho cc bc trong cc pha phn tch v thit k h ny. Thut ng quy trnh trong ti ny c hiu l bao gm cc bc trong cc pha phn tch v thit k phn mm. Mc d c nhiu phng php lun v cng c pht trin h a agent c xy dng nhng phng php lun MaSE (chi tit s c trnh by trong Chng 2) c la chn v hai l do sau y: a. Phng php lun MaSE k tha t phng php lun hng i tng v do s d dng hn cho nhng ngi pht trin phn mm quen thuc vi cch tip cn hng i tng ph bin hin nay; Phng php ln ny c cng c i km agentTool c th h tr pht trin t phn tch, thit k n sinh m ngun. Hn na, trong khi cc cng c khc tch bit khu pht trin ontology th agentTool tch hp khu ny vo trong qu trnh pht trin v do to iu kin d dng cho ngi pht trin hn v khng phi s dng cc cng c khc pht trin ontology v hn na n li c sinh ra trong qu trnh sinh m ngun h thng.

b.

Ni dung nghin cu ca ti bao gm:

Nghin cu cc c trng ca agent v h a agent; mt s vn c bn linquan n pht trin h phn mm agent bao gm xy dng ontology v tng tc;

Nghin cu cc bc trong phn tch v thit k h a agent v s dng cng cagentTool trong cc bc ny.

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Nghin cu p dng phng php lun MaSE trong phn tch v thit k h dchv thng mi in t TraNeS. Ti liu c t chc thnh 2 phn bao gm 7 chng nh sau:

Phn 1 C s pht trin h a agentChng 1: H a agent

Chng ny trnh by mt cch tng quan v agent, h a agent v cc cch tip cn trong nghin cu xy dng cc phng php lun pht trin h a agent. Ni dung ca chng ny tp trung xem xt cc cch tip cn khi xy dng cc phng php lun pht trin h phn mm a agent.Chng 2: Tng tc trong h a agent

Chng ny trc ht trnh by tng quan vn tng tc trong h a agent bao gm cc dng tng tc, tng tc vi agent trung gian v thng lng trong h a agent. Mt m hnh thng lng song phng da trn rng buc m s c trnh by nhm c s cho pht trin h dch v du lch s c cp n trong cc chng tip theo.Chng 3: Ontology trong h a agent

Ontology l khi nim quan trng nhm biu din ng ngha ca thng tin c truyn i gia cc agent trong qu trnh tng tc. Ni dung ca chng ny tp trung xem xt khi nim ontology v vai tr ca n trong tng tc gia cc agent. Phn k thut xy dng ontology trong h a agent s c cp trong Chng 4.Chng 4: Quy trnh pht trin h phn mm hng agent

Ni dung chng ny tp trung trnh by quy trnh pht trin h phn mm hng agent da trn phng php lun MaSE cng vi cc bc tng ng trong qu trnh pht trin da trn cng c agentTool. Cc bc pht trin ontology ca h thng cng c gi gn trong chng ny. Mt p dng ca quy trnh ny cho pht trin h dch v thng lng t ng s c m t chi tit trong cc chng cn li.

Phn 2: p dng pht trin h dch v du lchChng 5: Phn tch h dch v

Chng ny nhm trnh by chi tit mt p dng ca quy trnh pht trin h a agent cho phn tch h dch v du lch TraNeS. Ni dung cc bc phn tch ny c trnh by gn lin vi cng c pht trin agentTool.

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Chng 6: Thit k h dch v

Ni dung chnh ca chng ny l trnh by mt p dng ca quy trnh pht trin h a agent trong thit k cho thit k h dch v du lch TraNeS.Chng 7: Ci t v tch hp h dch v

Ni dung ca chng ny trnh by cc vn lin quan n ci t v tch hp h dch v thng lng.Chng 8: Gii thiu h TraNeS

Ni dung nhm im qua mt s c trng v cch tin hnh ci t ca h dch v du lch TraNeS c pht trin trong cc Chng 5, 6 v 7. Kt lun Phn cui cng l kt lun v mt s vn cn quan tm nghin cu hn na trong pht trin cc ng dng. Ti liu ny c vit vi gi thit rng ngi c quen thuc vi phng php lun pht trin phn mm hng i tng. Do , nhiu khi nim khng c nhc li nh use case, biu tng tc, biu trng thi. Mc d nhm ti c nhiu n lc hon thin ti liu nhng khng th trnh khi nhng thiu st. Rt mong nhn c nhng kin ng gp v ch bo ca cc ng nghip.

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MC LCLI GII THIU.........................................................................................................1 Phn 1 C s pht trin h a agent..........................................................................3Chng 1: H a agent.....................................................................................................3 Chng 2: Tng tc trong h a agent ..........................................................................3 Chng 3: Ontology trong h a agent............................................................................3 Chng 4: Quy trnh pht trin h phn mm hng agent.............................................3

Phn 2: p dng pht trin h dch v du lch..........................................................3Chng 5: Phn tch h dch v.......................................................................................3 Kt lun............................................................................................................................4

CHNG 1 .................................................................................................................9 H A AGENT............................................................................................................9 1.1 Agent................................................................................................................101.1.1 Khi nim agent.....................................................................................................10 1.1.2 Agent v i tng ...............................................................................................12

1.2 H a agent.......................................................................................................131.2.1 Khi nim h a agent...........................................................................................13 1.2.2 Mi trng tnh ton thch hp cho h a agent...................................................14 1.2.3 Cc ng dng ca h a agent...............................................................................15

1.3 Cc phng php lun pht trin h a agent...................................................16 1.3.1 Cc cch tip cn pht trin h a agent........................................................171.3.1.1 Cc phng php m hnh yu cu....................................................................18 1.3.1.2 Cc cch tip cn trong phn tch thit k h thng a agent............................19

1.4 Phng php lun Gaia.....................................................................................221.4.1 Gii thiu chung....................................................................................................22 1.4.2 Pha phn tch.........................................................................................................23 1.4.3 Pha thit k............................................................................................................23

1.5 Phng php lun MAS-CommonKADS.........................................................241.5.1 Gii thiu chung....................................................................................................24 1.5.2 Pha khi nim ho.................................................................................................25 1.5.3 Pha phn tch.........................................................................................................25 1.5.4 Pha thit k............................................................................................................27

1.4 Kt lun............................................................................................................28 CHNG 2................................................................................................................29 TNG TC ............................................................................................................29 TRONG H A AGENT...........................................................................................29 2.1 Tng quan v tng tc trong h a agent........................................................302.1.1 Ngn ng truyn thng gia cc agent..................................................................31 2.1.2 Cc m hnh tng tc..........................................................................................33 2.1.3 Tng tc vi agent trung gian.............................................................................37

2.2 Thng lng trong h a agent.......................................................................40 2.3 M hnh thng lng song phng................................................................422.3.1 C s ton hc cho thng lng song phng...................................................42 2.3.2 Chin lc thng lng cho agent bn...............................................................45 2.3.3 Chin lc thng lng cho agent mua..............................................................48

2.4 Kt lun............................................................................................................52 5

CHNG 3................................................................................................................53 ONTOLOGY TRONG H A AGENT....................................................................53 3.1 Khi nim Ontology.........................................................................................543.1.1 Khi nim..............................................................................................................54 3.1.2 Ontology v c s tri thc.....................................................................................55 3.1.3 Phn loi ontology.................................................................................................56 3.1.4 Vai tr ca ontology trong tng tc gia cc agent............................................57

3.2 Biu din ontology............................................................................................583.2.1 Biu din ontology theo kiu hnh thc................................................................59 3.2.2 Biu din ontology theo kiu khng hnh thc.....................................................65

3.3 Phng php lun xy dng ontology tng qut...............................................67 3.4 Kt lun............................................................................................................69 ....................................................................................................................................71 CHNG 4 ...............................................................................................................71 QUY TRNH PHT TRIN H PHN MM HNG AGENT............................71 4.1 c im ca phng php lun MaSE............................................................72 4.2 Quy trnh pht trin h phn mm hng agent................................................734.2.1 Khi qut cc bc pht trin................................................................................73 4.2.2 Pha phn tch.........................................................................................................75 4.2.3 Pha thit k............................................................................................................95

4.3 Kt lun..........................................................................................................105 CHNG 5 .............................................................................................................107 PHN TCH H DCH V.....................................................................................107 5.1 M hnh s thch ngi s dng.....................................................................108M hnh s thch v nhu cu ngi s dng l mt trong nhng vn then cht ca pht trin cc h thng v c bit cc h dch v thng mi in t. Mc ny dnh trnh by bi ton du lch m chng ti chn lm mu cho qu trnh pht trin h thng v sau xem xt vn m hnh s thch ngi s dng............................................108 5.1.1 Bi ton dch v du lch.......................................................................................108 5.1.2 M hnh s thch ngi s dng..........................................................................109 a. Rng buc cc thuc tnh..........................................................................................109 b. Rng buc gia cc mt hng...................................................................................111

5.2 Phn tch h thng .........................................................................................1125.2.1 Xc nh ch ca h thng.................................................................................112 5.2.2 Xy dng cc use case.........................................................................................114 5.2.3 Xy dng ontology..............................................................................................117 5.2.4 Hon thin cc role..............................................................................................119

5.3 Kt lun..........................................................................................................123 CHNG 6..............................................................................................................124 THIT K H DCH V.........................................................................................124 6.1 Mt s vn v thit k h a agent.............................................................125 6.2 Thit k h a agent .......................................................................................1266.2.1 Xy dng cc lp agent.......................................................................................126 6.2.2 Xy dng cc phin hi thoi..............................................................................127 6.2.3 Hon thin cc agent...........................................................................................132 6.2.4 Trin khai h thng..............................................................................................136

6.3 Kt lun..........................................................................................................136 CHUNG 7..............................................................................................................137 6

CI T V TCH HP H THNG...................................................................137 7.1 Vi nt v agentMom .....................................................................................138 7.2 M hnh tch hp h thng..............................................................................1407.2.1 UserAgent............................................................................................................140 7.2.2 HotelAgent v TrainAgent..................................................................................140 7.2.3 MatchAgent.........................................................................................................141 7.2.4 Hot ng ca h thng.......................................................................................142

7.3 Ci t cc lp agent.......................................................................................1437.3.1 UserAgent............................................................................................................143 7.3.2 HotelAgent..........................................................................................................149 7.3.3 TrainAgent...........................................................................................................153 7.3.4 MatchAgent.........................................................................................................156

7.4 Kt lun..........................................................................................................159 CHNG 8..............................................................................................................160 GII THIU H TRANES .....................................................................................160 8.1 c trng ca H TraNeS...............................................................................161 8.2 Cc m hnh hot ng ca h TraNeS...........................................................161 ..............................................................................................................................163 8.3 Cc nhm chc nng ca H TraNeS.............................................................165 8.5 Bi hc t pht trin h TraNeS......................................................................183 8.6 Kt lun..........................................................................................................185 KT LUN..............................................................................................................186

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PHN 1

C S PHT TRIN H A AGENT

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CHNG 1

H A AGENT Agent H a agent Mt s vn c bn khi nghin cu v pht trin h a agent Cc phng php lun pht trin h a agent

Ni dung chng ny trc ht trnh by mt cch khi qut v agent, h a agent, mi trng thch hp cho ng dng h a agent, v ba vn c bn cn quan tm khi nghin cu v pht trin h a agent l ontology, tng tc v phng php lun pht trin h a agent. Phn tip theo ca chng tp trung trnh by tng quan cc phng php lun trong pht trin h a agent nhm lm c s cho xy dng quy trnh pht trin h a agent s trnh by trong Chng 4.

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CHNG 1: H A AGENT

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1.1 Agent1.1.1 Khi nim agent Trong nhng nm gn y, s pht trin ca cc cng ngh Internet dn ti vic p dng rng ri ca cng ngh thng tin vo nhiu lnh vc khc nhau ca cuc sng nh tm kim truy xut thng tin, qun l mng vin thng, thng mi in t, h tr ra quyt nh, gii tr, S a dng ca cc lnh vc p dng khin cho vic pht trin phn mm cng ngy cng tr nn phc tp v s phc tp ny th hin mt s c im sau y: Khi lng cng vic cn x l ngy cng ln: Cc h phn mm ngy nay phi x l mt khi lng d liu rt ln hoc thao tc trn mt s lng ln cc ngun thng tin. Bn cnh , qu trnh pht trin h thng thng xuyn phi i mt vi cc bi ton c phc tp ln (nhiu bi ton thuc dng NP y ) c bit l vi cc ng dng thng mi in t hay iu khin phc tp. Yu cu v tnh chnh xc ngy cng cao: Yu cu ny xut hin cng vi s ra i ca cc h thng i hi chnh xc v thi gian thc nh cc h iu khin khng lu, iu khin thit b vin thng, cc bi ton qun l lu lng, qun l tin trnh cng vic c bit, vic xy dng v trin khai cc ng dng thi gian thc ang ngy cng tr thnh nhu cu tt yu v l mt trong nhng hng pht trin ca cng ngh thng tin v truyn thng ni chung. Yu cu v tnh m v phn tn: Yu cu ny xut hin cng vi s pht trin ca cc h thng mng, c bit l h thng trn mng Internet. Ngy nay, hu ht cc h thng thng tin u gn b cht ch vi mi trng mng. Internet tr thnh mt phn quan trng trong cuc sng con ngi v do cc phn mm cng cn phi p ng ngy cng tt hn cc nhu cu ca con ngi nh tm kim thng tin, h tr ngi mua v ngi bn a ra quyt nh,... v phi c tnh m, tc l c th c cp nht, thay i hay b sung cc dch v vo h thng. Yu cu tnh c lp cao gia cc thnh phn trong h thng: Yu cu ny th hin r nht trong cc h ra quyt nh v cc h thng mi in t. Cc h thng ny yu cu cc thnh phn phi hot ng c lp v ch ng tng tc vi cc thnh phn khc nhm hng ti ch ring ca mnh. Nht l trong cc h thng m mc ch ring ca cc thnh phn l khng thng nht vi nhau, thm ch tranh chp nhau th yu cu ny cng tr nn quan trng. Nhng yu cu ny dn n s nghin cu v pht trin mnh m ca cng ngh phn mm trong nhng nm gn y. Cch tip cn da trn cu trc chim u th vo nhng nm 70-80 dn dn b thay th bi phng php lun hng i tng vi

CHNG 1: H A AGENT

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tp k hiu chun UML m ngy nay tr thnh ph bin trong phn tch, thit k v xy dng cc h phn mm. Tuy nhin, khi h thng thng tin cng ngy cng phc tp th ngi ta cng nhn ra s hn ch ca cch tip cn ny. Nguyn nhn c bn l do tnh th ng ca cc i tng ngha l cc i tng ch thc s hot ng khi nhn c mt thng ip t i tng khc. Vi cc h thng c yu cu v tnh phn tn nh cc h thng lng trong thng mi in t, cc h qun l mng vin thngth tng tc th ng nh vy t ra khng ph hp. Cc thnh phn phn mm trong h thng nh vy phi phc v cho nhng dch v khc nhau v do cn phi ch ng theo mc ch ca ring mnh ng thi phi tng tc vi cc thnh phn khc chia s ti nguyn, yu cu h tr tnh ton... Ta th xt mt v d sau y. Trong h dch v du lch, ngi s dng thng c nhiu yu cu khc nhau cho cc gi du lch ca mnh nh v my bay, v tu, ch ...Do , thnh phn phn mm thay mt ngi dng cn phi tng tc, thng lng vi nhiu dch v khc mt cch t ng v sau tch hp kt qu gi li cho ngi s dng, mi thnh phn nh th c gi l mt agent. Mc d cho n nay cha c mt nh ngha thng nht v khi nim ny, nhiu nghin cu cho rng: Agent l mt h tnh ton hon chnh hay chng trnh c t trong mt mi trng nht nh, c kh nng hot ng mt cch t ch v mm do trong mi trng nhm t c mc ch thit k. Cc c trng c bn ca agent sau y c nhiu ngi tha nhn ([9], [13], [14], [20] ): Tnh t ch (autonomy): Mi agent c mt trng thi ring, c lp vi cc agent khc (tch trng thi bn trong) ng thi n c th t quyt nh cc hnh ng ca mnh (t ch v hnh ng). T ch trang thi bn trong th hin ch: mi agent cha mt trng thi no ca ring n, cc agent khc khng truy nhp c vo cc trng thi ny. Cn tnh t ch v hnh ng th hin ch agent c th t quyt nh cc hnh ng ca mnh (c th l mt hnh ng n hoc l mt chui cc hnh ng) da trn trng thi hin thi m khng c s can thip ca con ngi hay cc agent khc. Tnh t ch chnh l c trng quan trng nht ca agent.

Kh nng phn ng (reactivity): Tnh phn ng l kh nng agent c th nhn bit cmi trng (qua b phn cm nhn no ) v da qua nhn bit , agent p ng kp thi nhng thay i xy ra trong mi trng. Tnh phn ng th hin r nht cc agent hot ng trn cc mi trng c tnh m v hay thay i nh Internet, mi trng mng phn tn, mi trng vt l, Phn ng ca mi mt agent i vi mi trng bn ngoi u hng ti vic thc hin mc tiu (ch) ca agent .

CHNG 1: H A AGENT

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Tnh ch ng (pro-activeness): Khi c s thay i ca mi trng, agent khng ch phnng mt cch n gin m cn xc nh mt chui hnh ng cn thc hin, bn thn mi agent s ch ng trong vic khi ng v thc hin chui hnh ng ny.

Kh nng x hi (social ability): Cc agent khng ch hng ti ch ring ca mnh mcn c kh nng tng tc vi cc agent khc trong h thng hng ti ch chung ca h thng. Cc hot ng tng tc ny rt a dng bao gm phi hp, thng lng, cnh tranh

1.1.2 Agent v i tng hiu r hn khi nim agent, chng ta hy so snh agent v i tng. Trong phng php hng i tng, cc i tng c nh ngha l cc thc th tnh ton ng gi bao gm cc trng thi, cc hnh ng hay phng thc trong trng thi v cc i tng lin lc vi nhau thng qua vic gi cc thng ip (message). Xt theo quan im h thng, c th xem mi agent cng l mt i tng nhng mc tru tng cao hn. V vy, khi nim i tng c s dng trong phn ny l ch cc i tng chun (standard object) trong phng php hng i tng. Vi nh ngha agent c cp Mc 1.1.1 th cc i tng v cc agent c cc im khc bit sau: Agent c tnh t ch cao hn i tng. iu ny th hin ch cc agent c th t quyt nh hnh ng ca mnh m khng phi l thc hin hnh ng theo yu cu ca agent khc. Ngc li, cc i tng ch thc s hot ng khi nhn c li gi hm t cc i tng khc. Trong cc ngn ng lp trnh hng i tng nh Java chng hn, cc i tng c cc thnh phn ring kiu private khng th truy nhp t cc i tng khc. Tuy nhin, cc i tng li khng th t ch v mt hnh vi ca mnh, mt i tng vi thnh phn public, c th c truy nhp bi cc i tng khc v ch khi mt i tng khc s dng cc li gi ti cc thnh phn public ca i tng ny th n mi thc s hot ng. Agent c tnh hng ch, mi agent c mt ch ring v ch ca cc agent trong mt h thng c th thng nht hay khng tng thch vi nhau. Trong khi cc i tng khng c mc ch ring, chng cng chia s mc ch chung ca c h thng. Do , cc agent thng phi thng lng vi nhau trong qu trnh tng tc. Agent c cc hnh vi linh hot da trn cc c trng nh tnh ch ng, kh nng phn ng v kh nng x hi trnh by trn. Cn cc i tng th khng c cc kiu hnh vi ny.

CHNG 1: H A AGENT

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Mi agent c mt hoc nhiu lung iu khin (thread) ring. Trong h hng i tng cng c iu khin theo kiu lung (thread) nhng khng yu cu mi i tng l c thread ring m ngc li c th c nhiu i tng chung mt thread. Bn cht ca s khc nhau ny cng l c trng quan trng v mc t ch ca agent so vi i tng.

1.2 H a agent1.2.1 Khi nim h a agent Kh nng ca mi agent th hin nng lc gii quyt vn ca ring agent . Trong mt h thng c th, thng thng ti nguyn dnh cho mi agent l hn ch do kh nng hnh ng ca mi agent cng l hn ch. Mi agent ch tp trung gii quyt mt vn ti mt v tr c th no ch khng th gii quyt c ht cc vn t ra cho h thng. Trong cc h phn tn phc tp, h a agent c xem l h x l thng tin c nhiu ha hn. C th hiu h a agent l mt tp cc agent cng hot ng trong mt h thng, mi agent c th c ch khc nhau nhng ton b h agent cng hng ti mc ch chung thng qua tng tc. Qu trnh tnh ton v x l thng tin trong h a agent c xem l c nhiu u im hn so vi cc h thng khc nh h i tng [20]: Kh nng tnh ton hiu qu.: H a agent cung cp kh nng tnh ton hiu qu hn nh qu trnh tnh ton c phn chia cho cc agent khc nhau v kh nng phi hp cng x l ca nhiu agent. tin cy cao: Do c nhiu agent cng tham gia gii bi ton v cc agent c c ch trao i, kim tra kt qu nn tin cy tnh ton trong h a agent c cho l cao hn. Kh nng m rng: H a agent l h m v c th c thm cc agent mi hoc bt i cc agent khi cc agent hon thnh nhim v. Kh nng ny ph hp vi tnh m ca yu cu cc h phn mm hin nay. Tnh mnh m: H a agent c th x l c cc bi ton ra quyt nh phc tp hoc cc bi ton da trn thng tin khng chc chn nh cc bi ton thng lng trong thng mi in t, cc bi ton iu khin t ng... Kh nng bo tr: Do h a agent gm nhiu agent, mi agent l mt module c tnh t ch cao nn h a agent l h d bo tr. Kh nng phn ng: H a agent k tha kh nng phn ng ca cc agent n nn khi nhn bit c mt thay i ca mi trng th cc agent trong h thng s phi hp vi nhau a ra hnh ng tng ng vi thay i .

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Tnh linh hot: Cc agent trong h a agent c kh nng khc nhau c th tng tc vi nhau cng gii quyt mt vn chung. Mt agent trong h thng khng phi ch agent khc m ch ng tng tc tm ra thng tin cn thit gii quyt vn t ra cho ring mnh. Kh nng s dng li: H a agent c kh nng s dng li v mi agent c kh nng ring v c th dng li cho nhiu ng dng khc nhau.

1.2.2 Mi trng tnh ton thch hp cho h a agent H a agent t ra c nhiu u im trong vic gii quyt cc bi ton phc tp hin nay da trn tnh nng ca tng agent v s phi hp gia cc agent. Cc mi trng v dng bi ton thch hp cho h a agent bao gm [20]: H a agent c th gii quyt mt bi ton vt qu kh nng ca mt agent n. Trong h s dng mt agent n, h thng thng tp trung tt c cc x l cho mt agent duy nht. Nhng do ti nguyn ca mt agent n l hn ch (chng hn nh ng truyn hay b nh) nn cc h thng nh vy thng c nhng nt c chai, gy nghn mng hoc tnh trng b tc khi c qu nhiu yu cu tp trung v mt agent. H a agent gii quyt vn ny thng qua c ch phi hp, cng tc gia cc agent. H a agent cung cp phng php gii quyt cc bi ton phn tn trong c nhiu thnh phn t ch cng hot ng trong mt x hi agent (society of agent) v cng tun theo cc lut x hi (social law) trong x hi . Cc thnh phn trong cc h a agent khng phi lun lun c cng chung mt ch. thc hin cc ch ring ca mnh, cc agent c th tng tc vi cc agent khc theo cc giao thc tng tc nh: phi hp, cng tc, hoc trong trng hp mc ch ring mu thun nhau th c th l cnh tranh, thng lng. H a agent cung cp phng php gii quyt cc bi ton m thng tin c thu thp t nhiu ngun khc nhau. Cc ngun thng tin ny c bn cht phn tn trong mt h thng rt ln. V d c th cho dng bi ton ny chnh l bi ton truy xut thng tin trn internet, cc bi ton tch hp v x l thng tin Mt dng bi ton khc rt ph hp vi h a agent l bi ton tch hp h chuyn gia. Mi h chuyn gia l mt h thng tp trung gii quyt mt vn xc nh da trn tri thc ca chuyn gia v vn . Thc t c th c nhiu h chuyn gia tuy hng ti gii quyt cng mt vn nhng li phn tn nhng v tr rt xa nhau. H a agent cung cp kh nng phi hp gia cc h chuyn gia ny nng cao kh nng x l ca h thng. Cch tip cn hng agent ph hp khi h thng yu cu cc kiu lin lc phc tp, a dng. V d nh cc h thng s dng c ch lin lc ca con ngi hoc tng tc gia cc thc th hn tp.

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Cch tip cn hng agent ph hp cc h thng cn phi thc hin tt trong tnh hung khng th m t hnh vi ca cc thnh phn trong h thng mt cch r rng theo dng tng trng hp (case-by-case). Cch tip cn hng agent cng t ra ph hp trong tnh hung c s thng lng, cng tc hay cnh tranh gia cc thc th khc nhau trong h thng. V d nh cc tc v khc nhau vi cc ch xung t nhau c th cn phi thc hin ng thi, khi s c cc qu trnh cnh tranh hay thng lng gia cc thnh phn. Cch tip cn hng agent cng ph hp khi h thng phi hnh ng mt cch t ch thay mt ngi dng, v d nh trong cc qu trnh thng lng gia cc thnh phn bn trong h thng t ti nhng mc ch khc nhau.

1.2.3 Cc ng dng ca h a agent Trong nhng nm gn y, cc h a agent ngy cng tr nn ph bin v c p dng trong nhiu h thng khc nhau. Theo Jennings et al. [23], cc ng dng ca h a agent c th chia thnh cc nhm sau:Cc h ng dng trong cng nghip Cc ng dng h a agent trong cng nghip l nhng ng dng u tin ca lnh vc nghin cu ny. Hin nay, agent c p dng rng ri trong cc dng h thng nh:

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H sn xut: trong cc h a agent ng dng trong sn xut, cng vic s c phn chia thnh cc nhm cng vic hoc cc cng vic nh hn vo giao cho cc agent thc hin. Cc agent cn c c ch lp k hoch v phi hp (tng tc) ln nhau hon thnh cng vic c giao. H thng iu khin tin trnh: Cc h iu khin tin trnh c vai tr rt ln trong cng nghip. H a agent trong h thng ny s c xem nh mt b iu khin tin trnh (process controller) vi tnh t ch v linh hot iu khin hot ng ca tin trnh . H thng vin thng: cc h thng vin thng thng l cc h thng ln, phn tn, yu cu qu trnh gim st v qun l theo thi gian thc (nh qun l mng vin thng, gim st hot ng ca thit b). Cc ng dng ny rt ph hp vi h a agent. Ngoi ra, h a agent cng c p dng trong cc h thng qun l khng lu v qun l lu lng giao thng. y l cc h qun l yu cu tnh thi gian thc cao, cc thnh phn trong h thng phi c tnh t ch v linh hot trong x l tnh hung.

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Cc ng dng trong thng mi Trong thi gian gn y, h a agent ngy cng c p dng nhiu trong thng mi in t. Vi cc h ng dng ny, vic trao i mua bn din ra thun li v hiu qu

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hn cho c ngi bn, ngi mua cng nh cc nh sn xut. Cc h ng dng agent trong thng mi bao gm:

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H qun l thng tin: Cc h thng ny thc hin vic lc, tch v thu thp thng tin cn thit dng trong thng mi. H thng thng xuyn phi x l mt khi lng thng tin rt ln nhm cung cp cho ngi dng nhng thng tin cn thit. Cc h thng mi in t: Cc agent trong cc h thng mi in t s i din cho ngi bn, ngi mua cng nh ngi mi gii trong cc giao dch in t. Cc agent ny t trao i vi nhau thng qua cc chin lc thng lng ca mnh. y chnh l xu hng pht trin ca thng mi in t hin nay. Cc ng dng qun l tin trnh kinh doanh. Qun l tin trnh kinh doanh nhm gip cho ngi qun l ra quyt nh trong mt tnh hung c th hoc thc hin mt cng vic c th no vi s h tr ca tt c cc thnh vin trong n v. Cc agent s i din cho cc thnh vin thc hin cc vai tr xc nh. Cng vic s c phn chia cho cc nhm thnh vin da trn c ch tng tc gia cc agent.

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Cc ng dng gii tr Cc h a agent cng c s dng xy dng cc ng dng gii tr nh cc tr chi in t v cc ng dng khc nh nh ht hay rp chiu phim tng tc (Interactive Theatre and Cinema). Cc ng dng trong y t

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ng dng gim st bnh nhn. Cc agent hot ng nh cc chuyn gia theo di hoc chn on bnh cho ngi bnh. Vic chn on bnh c thc hin thng qua c ch lp lun ca agent. Cc ng dng chm sc sc kho (Health Care). H a agent c thit k thc hin cc nhim v ca mng li y t cng ng.

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1.3 Cc phng php lun pht trin h a agentTrong nghin cu pht trin h a agent ba vn sau y c quan tm xem xt:Tng tc gia cc agent

Trong cc h a agent, mi agent l mt thnh phn ch ng v hng ti ch ring nn cn phi trao trao i thng tin-tri thc vi nhau v thng lng vi nhau khi cn thit. Qu trnh trao i, tng tc gia cc agent khng th ging vi dng tng tc th ng (thng qua cc li gi hm) trong h hng i tng. Vn tng tc gia cc agent c xem l then cht trong pht trin h a agent v s c trnh by chi tit trong Chng 2.Ontology

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cc agent tng tc vi nhau thng qua vic gi v nhn cc thng ip truyn thng ging nh cc i tng. Tuy nhin, cc thng ip ny khng biu din cc li gi hm n gin m cn phi biu din c thng tin v tri thc trao i gia cc agent. Mi agent trong h a agent c th c mt min quan tm ring, cc agent hiu nhau trong qu trnh trao i cn mt cu trc ng ngha gi l ontology. Ontology v xy dng ontology biu din thng tin v tri thc trong h thng s c trnh by chi tit trong Chng 3.Phng php lun pht trin h a agent

Xy dng h a agent cn phi theo quan im no v cc bc no? Do xut pht im ca cc nh nghin cu khc nhau (hoc l t cng ng tr tu nhn to hoc l t gii nghin cu hng i tng) nn c nhng quan im khc nhau v pht trin h a agent. iu ny dn ti vic c nhiu phng php lun pht trin h a agent khc nhau; hoc da trn phng php lun truyn thng hng i tng hoc da trn cng ngh tri thc hoc c hai. Tng quan cc phng php lun pht trin h a agent s c cp tip theo trong phn ny. 1.3.1 Cc cch tip cn pht trin h a agent Nhu cu pht trin cc ng dng phn mm da trn cng ngh agent trong nhng nm gn y dn n s ra i ca nhiu phng php lun da vo ba cch tip cn sau y: (1) cch tip cn da trn agent v cng ngh agent, (2) cch tip cn pht trin t hng i tng v (3) cch tip cn da trn cng ngh tri thc. Ni dung phn cn li ca chng ny trc ht trnh by cc cch tip cn xy dng h a agent v mt s phng php lun c pht trin da trn cc cch tip cn . Sau , chng ti s tp trung trnh by khi qut hai phng php lun i din cho hai cch tip cn (1) v (2) l Gaia v MAS-CommonKADS. Qu trnh pht trin mt h thng phn mm thng thng bao gm cc pha chnh sau y: Xc nh yu cu Phn tch Thit k Ci t v tch hp

Trong cc pha trn th phn tch v thit k h thng c xem l cc pha chnh th hin quan im ca ngi pht trin v h thng ca mnh. Phn tip theo s trnh by mt s phng php m hnh yu cu ca ngi s dng, cc cch tip cn trong phn

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tch v thit k h a agent; phn ci t v tch hp cho mt p dng c th s c trnh by trong chng 7 ca ti liu ny. 1.3.1.1 Cc phng php m hnh yu cu Vic xc nh yu cu h thng l cng vic u tin cn thc hin khi xy dng mt h a agent. Phng php m hnh yu cu nhm m hnh v phn tch cc yu cu chc nng cng nh cc yu cu phi chc nng ca h cn pht trin. Tp cc yu cu cn phi c kh nng biu din y v chnh xc cc rng buc ca h thng trn thc t; n ng vai tr quan trng trong vic gim st cc thay i c th c trong ton b qu trnh phn tch thit k sau ny. Theo Weiss [37], c hai hng khc nhau trong vic m hnh ho yu cu h thng: (1) m hnh yu cu hng agent v (2) m hnh yu cu hng ch (goal). Chng ta s ln lt xem xt hai k thut ny.Phng php m hnh ho yu cu hng agent

M hnh yu cu hng agent da trn hai c im: Mi agent l mt phn mm c th c kh nng hot ng t ch v hng ti ch ring ca mnh. Agent c xy dng da trn vic m hnh qu trnh nhn thc v lp lun ca con ngi. Nh vy, mi yu cu cn phi xc nh c: h a agent nhm mc ch gii quyt nhng vn g; cn phi m hnh ho nhng tri thc no v nht l m hnh ho c ch lp lun ca agent da trn nhng c s no. Cc phng php i din cho kiu m hnh ny gm:i*: y l c s m hnh ho tp yu cu thng qua cc thuc tnh nh (intention) nh mc ch (goal) hay tho thun (commitment). Cc yu cu s c nhm theo cc thuc tnh nh ny v thng qua qu trnh m hnh ho chuyn sang giai on phn tch (v c t) yu cu. ALBERT (Agent-oriented Language for Bulding and Eliciting Real-Time requirement) v ALBERTII. y l cc k thut xc nh yu cu tp trung vo khi nim agent. ALBERT ng thi cng l mt ngn ng c t yu cu theo kiu hnh thc.

Hai kiu m hnh ho i* v ALBERT c th p dng ring bit hoc kt hp vi nhau. M hnh yu cu trong phng php lun Tropos ([2]) chnh l v d ca vic kt hp hai kiu ny.Phng php m hnh ho yu cu hng ch

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ch (goal) l khi nim tr li cu hi h thng hng ti ci g. Phng php m hnh ha yu cu hng ch s xc nh cc yu cu chc nng v phi chc nng theo phng php sau: Yu cu chc nng s c thu thp v nhm theo tr li ca cc cu hi ci g. Tc l cn phi tr li cc cu hi nh h thng hng ti thc hin cc cng vic g? cc thnh phn no cn c trong h thng? cc rng buc ca h thng l g?. Cc yu cu phi chc nng nhm m hnh ho cc cu hi ti sao, th no nh h thng thc hin nhim v ca mnh nh th no, ti sao cn h a agent? Cc v d ca phng php m hnh ho yu cu hng ch:KAOS (Knowledge Acquistion in automated Specification): l mt khun mu chung m hnh ho yu cu da trn tnh hng ch ca agent. NFR (Non-Functional Requirement): Tp trung vo vic c t v lp lun lin quan n cc yu cu phi chc nng. NFR cng xy dng phng php biu din cc yu cu softgoal, v d nh cc goal khng nh ngha mt cch r rng c, cc goal m t yu cu tho mn rng buc...

1.3.1.2 Cc cch tip cn trong phn tch thit k h thng a agent Theo [37] cc phng php lun phn tch v thit k h a agent u c xy dng da trn mt trong ba cch tip cn (Xem Hnh 1.1): Da trn agent v cng ngh agent Pht trin t phng php hng i tng Da trn cng ngh tri thc.

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Phng php lun pht trin h a agent

Cch tip cn da trn Agent v Cng ngh Agent:Cc khi nim tru tng mc x hi: Agent, nhm, t chc

Cch tip cn pht trin t hng i tngAgent: object c mc tru tng cao hn. M rng UML

Cch tip cn theo Cng ngh tri thcDa trn qu trnh nhn dng, thu nhn v m hnh ho tri thc

Hnh 1.1: Cc cch tip cn xy dng phng php lun a agent

Cch tip cn theo agent v cng ngh agent

Cc nghin cu xy dng phng php lun pht trin h a agent theo cc c trng ca agent v cng ngh agent xut pht t cc nhn nh sau: - Agent c nhng c trng ring nh tnh t ch, tnh ch ng v khnng phn ng. Cc c trng ny l khc hon ton khc vi i tng v to cho agent kh nng tng tc ch ng v kh nng suy lun m cc i tng khng c. V vy, khng th m hnh ho agent bng cch s dng cc phng php lun dnh cho hng i tng. - Agent hot ng nh mt x hi vi cc lut chi phi ring nn c th xem xt agent t kha cnh x hi v s dng cc khi nim tru tng mc x hi m hnh ho cc agent trong h thng.

Cc khi nim tru tng mc x hi c s dng m hnh ho agent theo cch tip cn ny bao gm agent, nhm (group), t chc (organization) ... Mc tru tng x hi c xem nh l mt mc tru tng cao hn so vi mc i tng thng thng v ph hp vi vic biu din cc agent v x hi cc agent bao gm cc thnh phn c tnh phn ng, linh hot v tng tc ch ng. Da trn cc khi nim tru tng mc x hi m phng php lun ny nh ngha cc bc, cc pha ca ton b qu trnh pht trin h thng. Thng thng, vi cch tip cn ny, qu trnh pht trin h thng c phn thnh hai pha tch bit: pha phn tch v pha thit k. Pha phn tch tng ng vi m

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hnh t chc (organization model) cn pha thit k ng vi m hnh agent (agent model). Tiu biu cho cc phng php lun thuc loi ny l cc phng php lun Gaia, SODA, AALAADINPhng php lun Gaia s c gii thiu chi tit hn trong phn 1.4.Cch tip cn pht trin t phng php hng i tng.

Khc vi cch tip cn trn, cch tip cn pht trin t phng php hng i tng da trn quan im cho rng cc k thut c pht trin v c p dng rng ri cho cng ngh phn mm hng i tng c th c m rng cho cc phn mm hng agent. Cch tip cn ny xem mi agent cng l mt i tng nhng mc tru tng cao hn. Cc cng c s dng biu din i tng v phn tch thit k h thng hng i tng nh UML hon ton c th m rng biu din cc c trng ring ca agent. Cc nghin cu xy dng phng php lun pht trin t phng php lun hng i tng tp trung vo cc cng vic sau: - Pht trin cc cng c da trn nn tng sn c ca hng i tng p dng cho h a agent, v d nh m rng UML thnh AUML (Agent UML). - B sung cc bc, pha mang tnh c trng ca agent v cng ngh agent nh ch (goal), vai tr (role) v ontology. Tiu biu cho cc phng php lun ny l cc phng php lun MaSE, MASSIVE, KGR...Cch tip cn da trn cng ngh tri thc

Da trn quan im cho rng qu trnh m hnh tri thc ring ca mi agent v s trao i tri thc gia cc agent trong h thng chnh l c s ca mi hot ng ca h thng, cc nghin cu theo cch tip cn ny s dng cc khi nim v qu trnh trong cng ngh tri thc xy dng nn phng php lun cho h a agent. Cc phng php lun ny tp trung vo cc qu trnh thu thp tri thc (Knowledge acquisition), m hnh tri thc (Knowledge modelling) v lp lun c s dng bi cc thnh phn agent trong h thng phn mm. Tiu biu cho cch tip cn ny l cc phng php lun nh CoMoMAS, MASComonKADS. Nh vy, c ba cch tip cn trong phn tch v thit k h a agent. Mi cch tip cn li c nhng u im ring. hiu nhng im khc bit ca cc phng php lun theo cc cch tip cn ny, phn cn li ca chng ny dnh trnh by v phng

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php lun Gaia (theo cch tip cn agent v cng ngh agent) v phng php lun MAS-CommonKADS (theo cch tip cn da trn cng ngh tri thc). Ring vi MaSE, i din cho cch tip cn pht trin t hng i tng, l phng php lun c la chn xy dng quy trnh pht trin h phn mm hng agent s c trnh by chi tit trong chng 4 ca ti liu.

1.4 Phng php lun Gaia1.4.1 Gii thiu chung Gaia [38] l mt phng php lun c xy dng theo cch tip cn agent v cng ngh agent. Phng php lun ny phn bit hon ton hai pha phn tch v thit k ng thi kt hp cc m hnh khc nhau trong cc pha . Gaia tp trung xem xt h a agent trn kha cnh t chc vi cc khi nim nh: vai tr (role), tng tc (interaction), v thu thp tri thc (acquaintance). Phng php lun Gaia tin hnh pht trin h thng da trn c hai quan im: quan im v m vi mc x hi (social level) v quan im vi m vi mc agent (agent level). Cc bc phn tch thit k trong Gaia l s chuyn tip gia cc m hnh trong qu trnh xy dng h thng. Mi quan h gia cc bc ny c biu din nh trong Hnh 1.2 :Tp yu cu (Requirement Statement)

M hnh vai tr (Role model)

M hnh tng tc (Interaction model)

PHA PHN TCH PHA THIT K

M hnh agent (Agent model)

M hnh dch v (Service model)

M hnh tri thc (Acquaintance model)

Hnh 1.2: Cc bc pht trin ca Gaia

Gaia cng mn mt s khi nim v k hiu t phn tch thit k h hng i tng. Tuy nhin, Gaia khng p dng cc phng php ny pht trin h a agent m cung cp mt tp cc khi nim mang tnh c trng ca agent gip cho ngi pht trin c th hiu v m hnh ho c cc h thng phc tp. Gaia gip ngi pht trin h thng xem qu trnh pht trin h agent nh l mt qu trnh thit k t chc (organisational design). Cc khi nim chnh trong Gaia c phn thnh hai nhm

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chnh l tru tng v c th. Cc khi nim tru tng bao gm role, quyn hn (permission), trch nhim (responsibilities), giao thc (protocol), hot ng (activities) cn cc khi nim c th l kiu agent (agent type), dch v (service) hay thu thp tri thc (acquaintance). Ta s ln lt xem xt chi tit cc pha phn tch v thit k trong Gaia. 1.4.2 Pha phn tch Mc ch ca pha phn tch l pht trin mt hiu bit c bn v h thng v cu trc ca n (khng xt chi tit n vic ci t h thng). Hiu bit ny c biu din theo cu trc t chc ca h thng. Chng ta c th xem cu trc t chc ca mt h thng bao gm mt tp cc role, cc mi quan h gia cc role v tng tc gia cc role . Khi nim role trong Gaia bao gm bn thuc tnh: trch nhim (responsibilities), quyn hn (permissions), hot ng (activities) v giao thc (protocols). Trch nhim xc nh cc yu cu chc nng ng vi role . Quyn hn ca mt role gip nhn ra cc trch nhim thng qua vic xc nh cc ti nguyn sn sng cho role . Cc hot ng ca role l cc tnh ton lin kt vi role m agent c th c th tin hnh m khng cn tng tc vi agent khc. Mi role cng c nh ngha bi mt s giao thc, mi giao thc xc nh role phi tng tc vi cc role khc nh th no. Da trn yu cu, pha phn tch s tin hnh xy dng m hnh role v m hnh tng tc gia cc agent trong h thng. M hnh role nhm xc nh cc role ca h thng v c biu din mt cch tru tng theo hai thuc tnh: - Cc quyn hn ng vi role - Cc trch nhim ca role M hnh tng tc xc nh s ph thuc v cc mi quan h gia cc role trong t chc a agent. Mi giao thc tng tc kt ni 2 role s c nh ngha c th trong m hnh ny. Tng tc trong m hnh ny c xem xt theo bn cht t nhin v mc ch ca tng tc ch khng phi da trn vic gi v nhn cc thng ip. 1.4.3 Pha thit k Mc ch ca pha thit k trong Gaia l chuyn cc m hnh trong pha phn tch sang mc tru tng thp hn (tng t nh trong thit k hng i tng) nhm hng ti vic ci t h thng. Ni cch khc, pha thit k nhm tr li cu hi lm th no x hi cc agent thng qua tng tc t c ch ca h thng, v ring vi cc agent th cn nhng g t c iu .

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Pha thit k trong Gaia bao gm ba m hnh: m hnh agent xc nh cc kiu agent trong h thng v cc agent c th trong h thng s l cc th hin ca cc kiu agent ny; m hnh dch v xc nh cc dch v chnh cn c thc hin cc role trong kiu agent tng ng; cn m hnh thu thp tri thc nhm biu din lin lc gia cc agent khc nhau. Ta s xem xt c th tng m hnh:M hnh agent Mc ch l xc nh cc kiu agent c th s dng trong qu trnh pht trin h thng. Mt kiu agent l mt tp cc role. Trn thc t c th tn ti cc tng ng 1-1 gia cc role v cc kiu agent. Tuy nhin, iu ny l khng bt buc, ngi thit k c th chn mt s role mt s role c lin quan vo trong cng mt kiu agent cho ph hp. Vi mi kiu agent, ngi thit k c th xc nh s agent th hin c th c thng qua mt ch gii ghi bn di tn lp agent nh sau. Nu s ch gii c dng l mt s n th s c chnh xc n th hin, nu l m..n th s c t nht l m v nhiu nht l n th hin, nu l * c th c 0 n nhiu th hin, cn nu l + th c ngha l c t 1 n nhiu th hin. M hnh dch v Xc nh cc dch v kt hp vi mi role v c t cc thuc tnh chnh ca dch v . C th xem mi dch v l mt chc nng ca agent. Mi dch v s c cc thuc tnh nh u vo, u ra, cc iu kin u vo (pre-conditions) v cc iu kin u ra (post-conditions). Cc iu kin u vo v u ra xc nh cc rng buc cho dch v . M hnh thu thp tri thc Xc nh cc lin lc gia cc kiu agent tn ti. M hnh khng xc nh thng ip g c gi i v khi no gi i, m ch n gin l ch ra cc phin lin lc ang tn ti. Mc ch ca m hnh ny l nhm pht hin ra cc nt c chai c th c trong thi gian hot ng ca h thng. Mt m hnh c dng nh mt th vi cc node l cc kiu agent.

1.5 Phng php lun MAS-CommonKADS1.5.1 Gii thiu chung MAS-CommonKADS [21] l phng php lun m rng t CommonKADS p dng cho phn tch v thit k h a agent. y l mt phng php lun theo cch tip cn da trn cng ngh tri thc. Phng php lun ny thm vo CommonKADS cc k thut ca phn tch thit k hng i tng nh k thut m hnh ho i tng (Object Modelling Technique: OMT), thit k hng trch nhim (Responsibility Driving Design: RDD) v cc k thut m t giao thc agent nh

CHNG 1: H A AGENT

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ngn ng m t v c t (Specification and Description Language: SDL) v biu thng ip tun t (Message Sequence Charts). MAS-CommonKADS a ra cc m hnh sau: M hnh agent (Agent model: AM): biu din cc c tnh ca agent nh: kh nng lp lun, cc dch v, cc nhm agent v cc s phn cp cc agent. M hnh task (Task model: TM): biu din cc task m agent c th tin hnh, cc ch (goal), cc thnh phn M hnh chuyn gia (Expert model: EM): biu din tri thc cn cho agent t c ch ca n t ra. M hnh t chc (Organisation model: OM): biu din cu trc t chc x hi trong h a agent cn xy dng. M hnh phi hp (CoM): biu din cc phin hi thoi gia cc agent, cc tng tc v cc giao thc tng tc tng ng. M hnh lin lc (Communication model: CM): biu din chi tit cc tng tc gia con ngi vi h thng a agent. M hnh thit k (Design model: DM): tp hp t cc m hnh trc thit k h thng. Bao gm ba m hnh nh: thit k mng, thit k agent v thit k nn.

Cc bc pht trin h a agent theo phng php lun MAS-CommonKADS bao gm 3 pha chnh l: pha khi nim ho, pha phn tch v pha thit k. Chng ta s ln lt xem xt cc pha ny. 1.5.2 Pha khi nim ho Nhim v chnh ca pha ny l m t bi ton thng qua cc biu use cases v scenario c dng tng t nh trong phn tch hng i tng. Cc biu ny gip chng ta hiu r cc yu cu phi hnh thc ca h thng v kim tra h thng v sau. Mi thnh phn tham gia vo cc use case v biu tun t c gi l mt role. 1.5.3 Pha phn tch Mc ch ca pha phn tch l c t cc yu cu ca h thng vo trong cc m hnh c ch ra trong phn 1.5.1 tr m hnh thit k. Qu trnh xy dng cc m hnh ny c m t ngn gn nh sau.

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Xy dng M hnh agent Cc agent s c xc nh theo cc chin lc sau: - Phn tch cc thnh phn tham gia vo cc use case xc nh trong pha khi nim ho nhm cc role tng t nhau vo trong mt agent nhm n gin ho cc trao i, lin lc trong h thng.

- Phn tch cc cu trong m t bi ton tm ra cc ch ng l cc i tng chng v gn chng thnh cc agent. Cc hnh ng ca cc ch ng ny s tr thnh ch ca agent nu nh hnh ng do agent khi to, v s tr thnh dch v ca n nu nh hnh ng c thc hin theo yu cu bn ngoi.

- S dng chin lc heuristics: cc agent s c xc nh thng qua cc khi nimv khong cch nh: s phn tn tri thc, phn tn v a l, phn tn v mt logic hoc phn tn v t chc.

- S dng m hnh chuyn gia xc nh cc chc nng v cc yu cu v nng lcx l tri thc, thng qua nh ngha cc agent. - S dng th CRC v k thut RDD ging nh trong thit k hng i tng. Xy dng M hnh Task Cc task c xc nh theo cch tip cn t trn xung v c biu din theo dng hnh cy. M t mt task bao gm tn ca task, u vo v u ra ca task, cu trc ca task, cc iu kin thc hin, M hnh ny gip ngi pht trin h thng d dng qun l cc thay i trong cc bc cn li ca pha phn tch cng nh trong pha thit k. Xy dng M hnh phi hp M hnh phi hp c xy dng theo 2 pha: - nh ngha cc knh truyn thng gia cc agent v xy dng mt bn mu (prototype). - Phn tch cc tng tc v ch ra cc tng tc phc tp cng vi cc giao thc phi hp tng ng. Mi pha bao gm mt lot cc bc nh, trong s dng cc k hiu theo MSC (Message Sequence Chart), SDL (Specification and Description Language) hoc biu din thng qua cc cu trc tri thc (tham kho thm trong [21]). Xy dng M hnh tri thc Ngi pht trin s s dng m hnh chuyn gia m hnh ho kh nng lp lun ca cc agent trong vic thc hin cc task v hng ti ch ca n. y ch c mt s m hnh chuyn gia c xy dng nhm m hnh ho kh nng lp lun trong min tri thc v m hnh ho kh nng suy lun ca agent.

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M hnh chuyn gia biu din cc tri thc ng dng (bao gm tri thc min, tri thc lp lun, v tri thc tc v) cng vi tri thc gii quyt bi ton. Qu trnh xy dng m hnh tri thc s ln lt xem xt v biu din cc tri thc ng dng v cc tri thc gii quyt bi ton. Xy dng M hnh t chc Tng t nh trong CommonKADS, m hnh t chc trong MAS-CommonKADS cng c xy dng biu din cc mi quan h tnh hoc c cu trc ho gia cc agent (trong khi m hnh phi hp biu din cc mi quan h ng). M hnh t chc cng s dng tp k hiu theo OMT nhng vi ng ngha thay i cho ph hp vi h a agent.

1.5.4 Pha thit k Da trn tp cc agent cng vi cc m hnh c xy dng trong pha phn tch, pha thit k s tin hnh xy dng m hnh thit k. Pha ny bao gm cc bc nh sau: - Thit k kin trc mng agent (agent network design) - Thit k agent (agent design) - Thit k nn (platform design) Ta s ln lt xem xt tng bc ny.Thit k kin trc mng agent Bc ny xc nh c s h tng cho h a agent bao gm cc iu kin cn thit v mng, v tri thc v cc s phi hp gia cc thnh phn trong h thng. Cc agent cng s c nh ngha trn c s h tng ca h thng ph thuc vo mt s iu kin cn thit theo yu cu sau: Cc iu kin v mng: bao gm dch v t tn agent, dch v ng k, mc bo mt, m ho v chng thc, cc giao thc truyn thng v ng dng... Cc iu kin v tri thc: bao gm cc ontology server, cc b chuyn i ngn ng m t tri thc... Cc iu kin v s phi hp gia cc thnh phn trong h thng: bao gm cc giao thc phi hp, cc dch v qun l nhm agent... Kt qu ca bc thit k kin trc mng agent l cc agent phi lin lc c vi nhau thng qua cc giao thc tng tc v ontology ca h thng. Thit k Agent Bc ny xc nh kin trc ph hp nht cho mi agent da theo cc module: lin lc vi ngi dng (user-communication), lin lc gia cc agent (agent communication), nng lc x l v cc dch v ca h thng.

-

-

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Thit k nn Bc ny la chn mi trng pht trin cho h a agent v cc phn cng cn thit cho h thng nu cn.

1.4 Kt lunChng ny trc ht tp trung trnh by nhng nt khi qut v agent, h a agent, nhng ng dng ca h a agent. Mt s so snh gia agent/h a agent v i tng/h i tng cng c im qua nhm lm sng t hn cc khi nim ny. Tip theo l im qua mt s vn quan trng khi nghin cu v pht trin h agent: ontology, tng tc v cc phng php lun. Phn quan trng ca chng ny l trnh by tng quan cc phng php ln pht trin h a agent nhm lm c s cho xy dng quy trnh pht trin h a agent da trn phng php lun MaSE m s c trnh by chi tit trong Chng 4.

CHNG 2

TNG TC TRONG H A AGENT

Tng quan v tng tc trong h a agent Thng lng trong h a agent M hnh thng lng song phng

Chng ny tp trung trnh by vn tng tc trong h a agent. Trc ht s cp tng quan v vai tr tng tc trong h a agent v ngn ng truyn thng c s dng trong qu trnh trao i thng tin v tri thc gia cc agent. Phn tip theo s trnh by cc m hnh tng tc trong h a agent v c bit tp trung xem xt m hnh thng lng song phng vi rng buc m nhm lm c s cho pht trin h dch v du lch TraNeS s c trnh by trong cc chng 5, 6, 7, 8.

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CHNG 2: TNG TC TRONG H A AGENT

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2.1 Tng quan v tng tc trong h a agentH a agent bao gm nhiu agent t ch c th hot ng trn nhng my tnh khc nhau. Tuy nhin, cc agent thng phi trao i, tng tc vi nhau v chnh cc tng tc trong h a agent quyt nh kin trc ca h thng . Cc dng tng tc ny phc tp hn rt nhiu so vi cc tng tc trong h i tng. Cc agent tng tc vi nhau bng cch gi thng ip v bn cht ca cc thng ip ny cng l nhng li gi hm nh trong h cc i tng nhng cc li gi trong tng tc gia cc agent c nhiu khc bit so vi tng tc gia cc i tng: Cc tham s c th c kiu c nh ngha trong mt cu trc ng ngha gi l ontology. Cc tham s c vit theo mt dng thng ip truyn thng c nh ngha bi mt ngn ng truyn thng agent (nh KQML hoc FIPA-ACL). Ni dung ca thng ip trong tng tc a agent c th rt phc tp nh mt chui cc hnh ng hoc cc yu cu

Ngoi s khc nhau v dng ca cc i s, tng tc trong h a agent cng khc tng tc gia cc i tng do bn cht khc nhau gia i tng v agent. Agent l thnh phn c tnh t ch v hnh ng hng ch ch khng th ng nh cc i tng. Vi mi h agent c th c xy dng th mc ch chung ca h thng v mc ch ring ca tng agent c th khc nhau, thm ch khng tng thch nhau. V d trong h thng mi in t, nu agent mua c nhim v mua c hng vi gi cng r cng tt th agent bn li c mc ch l bn vi gi cng cao cng tt. S thng nht v mu thun v mc ch ca cc agent trong h thng dn n s a dng ca cc m hnh tng tc trong h a agent. Nh vy, tng tc trong h a agent c nhng c trng ring khc bit so vi tng tc a i tng. Vai tr ca tng tc trong h a agent c th c tng kt nh sau: Thng qua tng tc, mi agent s thu thp thng tin v tri thc nhm t c ch (goal) ring ca mnh v hng ti ch chung ca c h thng. Tng tc to nn tnh ng cho h a agent. Qua tng tc, h thng c th c m rng hay thu hp mt cch d dng, nht l vi cc h a agent s dng agent trung gian.


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Qu trnh tng tc khng ch din ra gia cc agent m cn c th din ra gia cc h agent khc nhau. Khi , kh nng phi hp gia cc h thng gii quyt cc vn phc tp tng ln nhiu ln. Tng tc gia cc agent quyt nh kin trc v hot ng ca h a agent . Thng qua vic xem xt cc tng tc cn c gia cc agent, ngi thit k h thng c th xy dng kin trc h thng v phn tch nhim v mt cch r rng cho tng agent. Tng tc gia cc agent gip tch hp cc ngun thng tin trong h thng. Trong h tch hp thng tin, mi agent i din cho mt ngun thng tin nht nh. Cc ngun thng tin ny thng l khng ng nht, c biu din theo nhng cch khc nhau. Thng qua tng tc, thng tin gia cc ngun s c tch hp thu c nhng thng tin cn thit.

Ba vn sau y cn quan tm xem xt khi nghin cu v tng tc trong h a agent: 1. M hnh tng tc: Tu thuc vo mc ch ca h thng c th m ngi pht trin h thng phi la chn mt m hnh tng tc ph hp, m hnh tng tc ny s quy nh kin trc ca h thng cng nh hnh vi ca cc agent trong h thng. Ngn ng truyn thng s dng trong cc thng ip: Khi hot ng trong cng mt h thng vi nhau cc agent phi s dng chung mt ngn ng truyn thng. Ngn ng ny khng ch quy nh cu trc thng ip m cn quy nh cc dng thng ip hi v tr li trong cc phin hi thoi. Ontology v s dng ontology trong tng tc a agent: Mi agent trong h thng l mt thnh phn phn mm ring bit, do , min tri thc quan tm ca cc agent trong mt h thng c th khc nhau. cc agent c th hiu nhau trong qu trnh trao i th h thng phi s dng ontology nhm biu din cc khi nim m t min v mi quan h gia cc khi nim . Phn 2.1.1 s trnh by nhng nt chung v ngn ng truyn thng a agent. Cc m hnh tng tc s c trnh by trong phn 2.3. Ontology s c trnh by trong chng 3. 2.1.1 Ngn ng truyn thng gia cc agent Cc agent trao i vi nhau thng qua cc thng ip. Khc vi h hng i tng, thng ip trong h a agent khng ch biu din cc li gi hm m cn phi biu din thng tin v tri thc cn trao i gia cc agent. Cc thng ip ny c biu din theo cc ngn ng truyn thng agent (ACL: Agent Comminucation Language) nhm mc ch:

2.

3.


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thng.

nh ngha khun dng cc thng ip trao i gia cc agent trong h

Thit lp mt giao thc trao i gia cc agent, bao gm: nh ngha cc kiu thng ip gi v nhn, cc m hnh trao i thng ip gia cc agent. Cc ngn ng truyn thng u da trn l thuyt hnh ng - li ni (speech-act) ([11]). Mi thng ip bao gi cng phi m t y ngi gi, ngi nhn, mc ch ca li ni v ng ngha ca li ni. Mt hnh ng - li ni y khng ch nh ngha cu trc li ni m cn xc nh hnh ng lin quan n li ni . C nhiu ngn ng truyn thng a agent c a ra trong hai ngn ng truyn thng c s dng rng ri nht nht l KQML ([11]) v FIPA-ACL ([10]). KQML (Knowledge Query and Manipulation Language) y l mt ngn ng c pht trin theo d n DARPA trong khong thi gian u nhng nm 1990 [11]. KQML nh ngha ngn ng v giao thc cho qu trnh chuyn i thng tin v tri thc trong h a agent. KQML nh ngha ba mc l mc ni dung, mc thng ip v mc truyn thng. Mi thng ip KQML nh ngha mt hnh ng thoi, ng ngha i km hnh ng thoi , giao thc v mt tp cc thuc tnh. Cu trc chung ca mt thng ip KQML nh sau(performative-name : sender : receiver : content : language : ontology : reply-with : in-reply-to A B X L N W P)

Mi mt thng ip KQML tng ng vi mt dng tng tc trong trng performative-name. C ti 25 dng tng tc (performative) c nh ngha bao gm ask-one, advertise, broadcast, insert... ng thi, KQML cho php m rng v nh ngha thm cc dng tng tc khc khi cn thit. Trng content m t ni dung ca thng ip. Ni dung ny c th rt phc tp tu thuc vo nhu cu trao i thng tin ca hai agent trong phin lin lc . Agent nhn s hiu c ni dung trong trng content bng cch tham chiu vo trng ontology ca thng ip m n nhn c. KQML cng nh ngha cc


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giao thc truyn thng bao gm c th t cc thng ip, cc perormative. V d mt giao thc truyn thng c nh ngha trong KQML nh Hnh 2.1:

Fbroker(ask(X)) tell(X)

advertise(ask(X))

A

tell(X)

ask(X)

B

Hnh 2.1: Mt giao thc truyn thng trong KQML

FIPA-ACL (Foudation for Intelligent Physical Agent) FIPA-ACL (Foundation Intelligent Physical Agent) l ngn ng truyn thng agent c pht trin nm 1997. FIPA-ACL cng da trn l thuyt hnh ng li ni v c cu trc tng t nh KQML. FIPA-ACL s dng XML theo dng nh sau [10]:

So vi KQML, FIPA-ACL linh ng hn v c th d dng thm vo cc dng tng tc mi. Tuy nhin, FIPA-ACL khng nh ngha cc performative theo kiu s dng thnh phn trung gian (facilitator) nh trong KQML. l cc performative nh broker hay advertise. 2.1.2 Cc m hnh tng tc Phn loi m hnh tng tc Da vo mc ch ca cc bn tham gia tng tc, c th chia cc hnh thc tng tc thnh hai loi chnh: Hp tc v cnh tranh ([20]). Hp tc: Hai bn cng thc hin mt cng vic chung (cng tc) hoc cng vic ca

bn ny l bc tin cho bn kia (Phi hp). Hnh thc tng tc ny thng xut


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hin khi cc agent c chung mc ch, nhim v hoc cng thc hin mt tin trnh phc tp nht nh. Cnh tranh: Hai bn cnh tranh nhau v thng tin, hoc quyn li (thng lng)

hoc hon ton tri ngc nhau v li ch (i u). Nh vy, c th c cc loi hnh tng tc nh sau:Tng tc

Hp tc

Cnh tranh

Phi hp

Cng tc

Thng lng

i u

Hnh 2.2: Cc loi hnh tng tc

Phn 2.3.2 s trnh by mt s m hnh tng tc theo cch phn loi ny. Mt s m hnh hp tc Cc giao thc phi hp Trong cc mi trng phn tn v hn ch v ti nguyn cho cc agent th cc agent thng phi phi hp vi nhau. Nh trnh by trong phn 2.2.1, m hnh tng tc c coi l phi hp khi cng vic ca agent ny l tin cho cng vic ca agent kia. cc agent phi hp vi nhau, cc nghin cu cho rng cn xy dng k thut phn tn cng vic cn thc hin, bao gm c phn tn v iu khin (control) v phn tn d liu (data). Phn tn v iu khin tc l cc agent c th t ch trong vic sinh ra cc hnh ng mi v quyt nh mc ch k tip hng ti vic thc hin cng vic chung. Tri thc ca h thng trong trng hp ny cn c bit bi tt c cc thnh phn trong h thng. Da trn tri thc ny, cc agent s xc nh hnh ng tip theo cn thc hin trong mt chui cng vic cn thit hoan thanh muc tiu chung cua h thng.


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Lin quan n m hnh phi hp cn nhiu vn khc nh s tho thun (commitment), cc quy c (conventions) v vic biu din cc tho thun hay cc quy c ny ([20]) Cc giao thc cng tc Chin lc chung ca cc giao thc cng tc l phn r nhim v cn thc hin ca c h thng v sau phn tn cc tc v (task) c th cho cc thnh vin. Cc agent cng hng ti ch chung thng qua vic thc hin cc tc v m mnh c giao. Vic phn r cc task nh th no c thc hin bi ngi thit k h thng v tun theo cc giao thc c th. Cc tc v c phn r phi tho mn cc yu cu sau: Trnh xung t ti nguyn Cc tc v phi ph hp vi kh nng ca agent To ra mt agent c nhim v phn phi tc v cho cc agent khc trong h thng. Xc nh cc tc v c c lp cao gim thiu vic truyn thng v ng b ho kt qu. nh ngha li cc tc v nu cn thit hon thnh mt tc v khn cp.

Phn tip theo s trnh by hai giao thc cng tc tiu biu l giao thc mng hp ng v giao thc bng en.Giao thc Mng hp ng

Giao thc mng hp ng l mt giao thc tng tc kiu cng tc. Giao thc ny s kt hp cc kt qu t cc agent khc nhau thng qua vic m hnh ho h thng theo c ch hp ng s dng trong thng mi trao i sn phm v dch v. Mng hp ng s cung cp gii php cho bi ton: tm mt agent ph hp cho mt tc v cho trc. Gi s c mt agent c mt tc v cn x l. Agent ny s c gi l manager, v agent c kh nng x l tc v ny gi l contractor. Tng tc gia manager v contractor s din ra theo biu tng tc sau:


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Manager

Contractor

Thng bo tc v cn thc hin Phn hi nh gi kh nng thc hin task Xc nhn mt hp ng cho contractor ph hp Thc hin tc v v tr li kt qu Kt thc tc vHnh 2.3: Giao thc mng hp ng

Manager s gi thng bo v tc v cn thc hin cho tt c cc agent khc trong h thng. Khi nhn c yu cu, cc agent s gi tr li cho manager thng bo v kh nng thc hin tc v ca mnh. Manager s nh gi v chn ra agent ph hp nht thc hin tc v v xc nhn agent thnh contractor. Contractor s c nhim v thc hin tc v v tr li kt qu cho manager. Trn l thuyt, manager c th l bt k agent no trong h thng khi c task cn thc hin. V vy mi agent c th nhn c nhiu task, nu agent l agent c kh nng x l cao th rt nhiu manager s chn agent lm contractor. Khi , contractor s la chn task hp dn nht v m hnh mng hp ng s tr nn phc tp hn nhiu. Giao thc Bng en Phng php gii quyt bi ton da trn giao thc Bng en c m t nh sau: Gi s c mt nhm chuyn gia hoc agent cng ngi cnh mt bng en ln. Cc chuyn gia s cng tc vi nhau gii quyt bi ton thng qua vic s dng bng en pht trin li gii. Qu trnh gii bi ton bt u khi bi ton v d liu u vo c vit ln bng en. Cc chuyn gia s quan st bng en v c gng a ra kin pht trin li gii ca bi ton. Khi tm ra c mt thng tin/ kin ph hp, chuyn gia ny s vit kin (thng tin) ln bng en. Cc chuyn gia khc s s dng thng tin ny tip tc tm ra li gii. Qu trnh c tip tc nh vy cho n khi bi ton c gii quyt hon ton.


37

p dng giao thc bng en cho h a agent ta s c m hnh tng tc kiu bng en. Khi , h thng ny c cc c im sau: - Tnh c lp v gii php: Cc chuyn gia c th a ra cc kin c lp vi nhau. - Tnh a dng trong k thut gii bi ton: Thng qua bng en v cc phng php biu din tri thc th mt bi ton c th c rt nhiu hng gii quyt khc nhau. - Cho php biu din thng tin mt cch linh hot trn bng en. - S dng ngn ng tng tc chung. Mt giao thc kt hp cng tc v cnh tranh l thng lng s c trnh by chi tit trong phn 3.2 v 3.3 ca ti liu. Phn tip theo dnh trnh by kin trc agent trung gian. 2.1.3 Tng tc vi agent trung gian 2.1.3.1 Vai tr ca agent trung gian Trn quan im ch trng n cc m hnh c s dng agent trung gian, ta c th chia cc m hnh tng tc trong h a agent thnh: (i) tng tc vi agent trung gian v (ii) tng tc khng s dng agent trung gian. Cc m hnh tng tc khng s dng agent trung gian nh m hnh bng en, mng hp ng c u im l n gin, d xy dng v ph hp vi nhng h thng a agent ng. Cc m hnh ny yu cu cc agent phi bit c kh nng ca cc agent khc trong h thng m n mun tng tc. Do , h thng vi cc m hnh ny kh m rng cho agent khc tham gia nh trong mi trng Internet. Khc vi cc m hnh bng en hay hp ng, m hnh tng tc vi agent trung gian ([24], [35], [40]) s dng mt agent trung gian MidAgent nhm qun l kh nng ca cc agent khc. Trong m hnh ny, Agent Yu cu (Requester Agent) s tng tc vi MidAgent bit c kh nng ca cc agent (Agent Cung cp: Provider Agent) trong h thng c th gii quyt c yu cu ca mnh . Vai tr ca MidAgent trong nhng m hnh c th c th khc nhau nhng lp agent ny u c chung nhng c trng sau: Cung cp cc phng tin dch v c bn qun l x hi cc agent; Phi hp cc dch v c cung cp theo mt giao thc xc nh no ; m bo qun l cc agent bn trong x hi agent v qun l vic thm hay bt cc agent tham gia vo h thng.


38

Trong [24], lp m hnh tng tc s dng agent trung gian c chia ra thnh 3 m hnh nh gm m hnh tng tc kiu Agent Trung tm (Mediator Agent), m hnh tng tc kiu Mi gii (MatchMaker) v m hnh tng tc kiu iu phi (Broker). 2.1.3.2 Cc m hnh tng tc vi agent trung gianM hnh tng tc vi Agent Trung tm (Mediator Agent) Trong m hnh ny, nhim v ca Agent Trung tm l ch ng lin lc vi cc agent khc c d liu hay tri thc cn thit trong h thng. Cc dch v m Agent Trung tm c th cung cp l: T ng xc nh cc dch v thng tin; Xc nh vai tr ca cc agent trong h thng;

T thu thp v to ra thng tin t cc Agent Cung cp (Provider Agent) sau gi tr licho cc agent yu cu. thc hin nhim v trn, Agent Trung tm s dng m hnh thng tin ton cc bng cch thu thp v tch hp cc thng tin cn thit gii quyt cc yu cu hoc c th chuyn yu cu cho cc agent ph hp trong h thng gii quyt. Nh vy, Agent Trung tm ng vai tr va l agent trc tip qun l cc agent khc li va t tm ra thng tin cn thit gii quyt v gi tr li kt qu cho cc agent yu cu. Cng vic ca Agent Trung tm l rt nhiu v hiu qu hot ng ca h thng ph thuc hon ton vo kh nng ca agent ny. Vai tr ca MidAgent s gim i trong hai m hnh cn li c trnh by sau. M hnh tng tc vi Agent iu phi (Broker Agent) Trong m hnh ny, MidAgent ng vai tr l Agent iu phi (Broker Agent). Cng vic m Agent iu phi cn thc hin l mt phn cng vic ca Agent Trung tm v c biu din nh trong Hnh 2.4. Khi c mt agent mi tham gia vo h thng, th n phi ng k kh nng cung cp dch v ca mnh cho Agent iu phi. Dch v, tn v a ch ca Agent Cung cp ny s c cp nht vo c s tri thc ca Agent iu phi.


39

1: Yu cu dch v

Agent Yu cu

5: Tr li kt qu dch v

Agent iu phi

0: ng k, hu ng k dch v

Agent Cung cp

3: Yu cu dch v v giao tc

4: Chuyn kt qu dch v

Hnh 2.4: M hnh tng tc s dng Agent iu phi

Khi c mt agent Agent Yu cu gi cho Agent iu phi mt yu cu dch v no , Agent iu phi s tm kim trong c s tri thc ca mnh xem c Agent Cung cp no c th gii quyt c yu cu ca Agent Yu cu khng v sau lin lc trc tip vi agent gii quyt yu cu. Sau cng, Agent iu phi s gi li kt qu cho Agent Yu cu v kt thc qu trnh tng tc. Nh vy, trong m hnh tng tc ny, bt c mt lin lc no gia Agent Yu cu v Agent Cung cp u phi thng qua Agent iu phi. Trong mt s ti liu, Agent iu phi cn c gi l Facilitator ([40]). u im ca m hnh ny l kh nng m rng h thng. Mt agent mi mun tham gia vo h thng th agent ch cn ng k dch v vi Agent iu phi. Tuy nhin, nhc im ca m hnh ny l Agent yu cu phi gi i ton b yu cu ca mnh cho Agent iu phi m iu ny thng khng thc t c bit trong thng mi in t. M hnh tng tc vi Agent Mi gii (MatchMaker Agent) Trong m hnh ny, MidAgent ng vai tr nh mt Agent Mi gii m nhim v chnh ca n l to ra c ch lin lc trc tip gia Agent Yu cu v Agent Cung cp nh minh ho trong Hnh 2.5.


40

1: Yu cu dch v

Agent Yu cu

Agent Mi gii

2: Tr li tn agent cung cp 0: ng k, Hu ng k dch v

3: Yu cu dch v

4: Tr li kt qu dch v

Agent Cung cp

Hnh 2.5: M hnh tng tc s dng Agent Mi gii

Tng t nh m hnh Agent iu phi, khi mun tham gia vo h thng, mi agent phi ng k dch v vi Agent Mi gii v tr thnh nh cung cp dch v (Agent Cung cp). Agent Mi gii s cp nht vo c s tri thc ca n tn v kh nng dch v ca Agent Cung cp. Trong mt tng tc c th, khi c mt Agent Yu cu yu cu mt dch v, n s gi yu cu n Agent Mi gii. Agent Mi gii s xem xt trong c s tri thc ca n tm ra Agent Cung cp c th thc hin yu cu v s gi cho Agent Yu cu tn, a ch ca Agent Cung cp . Qu trnh tng tc sau s din ra trc tip gia Agent Yu cu v Agent Cung cp. Nh vy, cng vic m Agent Mi gii phi thc hin l mt phn cng vic ca Agent iu phi. Trong m hnh ny, Agent Yu cu ch cn gi i yu cu no lin quan n vic tm ra Agent Cung cp ph hp.

2.2 Thng lng trong h a agentKhc vi cc m hnh tng tc kiu cng tc nh mng hp ng hay bng en, thng lng l mt tin trnh tng tc va cng tc va cnh tranh c din ra gia hai hay nhiu bn tham gia, bt u bng nhng mc tiu (ch) khc nhau, dn dn i n mt tho thun chung c li cho tt c cc bn. Trong bi ton thng lng, tu vo s bn tham gia, ngi ta chia lm bn nhm l: thng lng 1-1, thng lng 1- n, thng lng n-1 v thng lng n-n. S phn chia ny c minh ho nh Hnh 2.6.


41

S ngi mua

Thng lng 1-1: cn gi l thng lng song phng, ch c mt ngi bn thng lng vi mt ngi mua. Thng lng n-1: nhiu ngi mua mt ngi bn. y chnh l hnh thc u gi (Auction). u gi l mt trong nhng hnh thc mua bn ph bin trong thng mi. Trong m hnh u gi (nhiu ngi mua, mt ngi bn), ngi mua s tr gi theo mt cch thc no , v d nh ai tr gi cao nht s thng. Thng lng 1-n: Mt ngi mua c th thng lng ng thi vi nhiu ngi bn. Hnh thc ny cn gi l u gi ngc (Reverse-Auction). Thng lng n-n: cn gi l thng lng a phng hay ch (market). Mi ngi mua c th thng lng ng thi vi nhiu ngi bn v mi ngi bn cng c th thng lng ng thi vi nhiu ngi mua. Khi h thng c cc agent i din cho ngi mua v ngi bn th cc agent ny s t ng thng lng vi nhau. Trong thng lng song phng ngi ta chia ra ba cch tip cn [5]:Cch tip cn da trn l thuyt tr chi

y l cch tip cn s dng chin lc tng tc gia cc agent ch k (selfinterested agent) theo cc lut tr chi. Trong cch tip cn ny, cc nh nghin cu c gng xc nh mt chin lc ti u bng cch phn tch mi tng tc gia cc agent ging nh trong mt tr chi v tm ra im cn bng ca qu trnh tng tc gia cc agent .Cch tip cn da trn Heuristic

S ngi bn

1-1 n-1

1-n n-n

Hnh 2.6: Cc dng thng lng


42

Trong m hnh ny, cc hm quyt nh da trn heuristic c s dng c

lng v sinh ra cc yu cu hay ngh mi trong qu trnh thng lng.Cch tip cn da trn lp lun (Argumentation-based)

Cch tip cn ny cho php cc agent c th chuyn cc thng tin thm hoc lp lun cho cc gi tr tinh thn nh nim tin hay nh trong qu trnh thng lng. Phn 3.4 ca ti liu s tm hiu mt kin trc thng lng s dng agent trung gian v p dng kin trc ny cho thng lng song phng cng nh thng lng a phng.

2.3 M hnh thng lng song phng2.3.1 C s ton hc cho thng lng song phng Ni dung phn ny trnh by cc khi nim c bn v logic m nhm lm c s cho vic m hnh ho chin lc thng lng da trn rng buc m s c trnh by trong phn 2.3.2.Tp m

Khi nim tp m nhm biu din v tnh ton vi cc d liu lin quan n bin ngn ng.nh ngha 2.1 ([12]): Cho X l mt tp khc rng. Mt tp m A trong X c c trng

bi hm lin thuc A : X [0,1]

v A ( x) c hiu l mc ph thuc ca phn t x vo tp m A, vi mi phn txX .

Cc hm lin thuc c th dng hnh thang hoc tam gic thng c chn cho nhiu ng dng thc t.


43

Hnh 2.7: Cc phng php c lng m: hnh thang v tam gic

Lt ct ca tp m nh ngha 2.2 ([26]): Gi A l mt tp m trong mt tp khng rng X vi hm thuc

A . Mt lt ct A (x) .

ca tp m A c xc nh l tp cc phn t

x X sao cho

Hnh 2.8 minh ho mt cch xc nh lt ct ca mt tp m.

Hnh 2.8: Xc nh lt ct ca tp m

Cc ton t m

nh ngha 2.3 ([26]): Mt hm tho mn bn iu kin.

G : [0,1] [0,1] [0,1]

c gi l hm u tin nu n

1. G (u1 , a ) G (u 2 , a ) nu u1 u 2 , 2. G (u , a1 ) G (u , a 2 ) nu a1 a 2 , 3. G(1, a) = a, 4. G(0, a) = 1. nh ngha 2.4 ([25]): Mt hm O : [0,1] [0,1] [0,1] c gi l hm ng nht u tin nu n tho mn cc iu kin. 1. O(u1 , ) O(u 2 , ) nu u1 u 2 , 2. O(u , 1 ) O(u , 2 ) nu 1 2 ,


44

3. O (1, ) = . nh ngha 2.5 ([26]): Mt ton t hai ngi : [0,1] [0,1] [0,1] c gi l ton t ng nht nu n n iu tng, i xng v tn ti mt phn t [0,1] sao cho [0,1] : a = a . Phn t khi c gi l phn t n v ca ton t ng nht a . Mt ton t ng nht vi phn t n v c cc tnh cht sau y [26]: 1. 2. 3. 4. 5.a a = a ,a b max( a, b) nu a, b > , a b min( a, b) nu a, b ,

0 a = 0.

nh ngha 2.6 ([26]): Mt hm F : [0,1] [0,1] [0,1] [0,1] c gi l hm chp nhn tng th ca ngi mua i vi mt mt hng nu n tho mn cc iu kin. 1. F (0, , ) = 0 v F ( ,0, ) = 0 , 2. F (1 , 1 , 1 ) F ( 2 , 2 , 2 ) nu 1 2 , 1 2 , 1 2 , 3. F ( , , ) min( , ) , 4. < F ( , , ) < 1 nu < , > 0 , l ngng chp nhn ca ngi dng.Ton t OWA

Ton t OWA (Ordered Weighted Average) l mt k thut kt hp da trn cc trng s c sp xp, do Ronald R. Yager gii thiu nm 1988.nh ngha 2.7 ([12]): Mt ton t OWA n chiu l mt nh x F : R n R xc nh bi

vector w = ( w1 , w2 ,... wn ) sao cho wi [0,1] , 1 i n vT

wi =1

n

i

= w1 + w2 + ... + wn = 1 .

F (a1 , a 2 ,... a n ) = w j b j = w1b1 + ... + wn bnj =1

n

vi bj l phn t ln th j ca tp A = (a1 ,... a n ) .

Mt s trng hp c bit ca ton t OWA [12].


45

Max: trong trng hp w* = (1,0,... 0) T th Max(a1,an) = max{a1,an}.T Min: trong trng hp w* = (0,0,... 1) th

Min(a1,an) = min{a1,an}.T Average: trong trng hp w A = ( n , n ,..., n ) th

1 1

1

FA (a1 ,... a n ) =

a1 + ... + a n . n

Mt ng dng quan trng ca ton t OWA l trong kt hp theo cc lng t ngn ng [12]. Gi s {A1, A2, ... An} l mt tp cc tiu ch nh gi mt lp cc i tng no v x l mt i tng thuc lp sao cho vi mi tiu ch Ai, gi tr hm Ai ( x) [0,1] ch ra tho mn ca i tng x i vi thuc tnh Ai. Nu mun tm mc tho mn tt c cc tiu ch ca i tng x, k hiu l D(x), th D(x) = Min{A1(x), A2(x), ... An(x)} Nu mun tm mc tho mn t nht mt tiu ch ca i tng x, k hiu l E(x), th E(x) = Max{A1(x), A2(x), ... An(x)} Trong cc trng hp cn li, tu theo lng t ngn ng m phi xy dng cc hm tm mc tho mn ca i tng x theo dng cc lng t n iu khng gim hoc lng t n iu khng tng (xem chi tit [12]). 2.3.2 Chin lc thng lng cho agent bn Trong m hnh thng lng song phng, agent bn c nhim v qun l vic giao dch ng thi vi cc khch hng ca mnh. Mi agent bn c trang b mt tp cc tri thc sau y: a. Tp O = {O1, O2, ... Om} cc n v hng ho c th cung cp, mi n v hng ho Oi (ca cng mt mt hng - mi agent bn ch bn mt mt hng) c m t thng


46

i i i qua n thuc tnh { o1 , o2 ,... on } v c mt gi tr li ch gi nu bn c n v hng

. b. Mt tp R = {r1, r2, ...rm} cc rng buc i vi ngi mua ca cc n v hng ho. Tp ny c min gi tr kiu boolean (c hoc khng). c. Mt tp C = {c1, c2, ...cn} cc hnh thc khuyn mi cho cc n v hng ho tng ng, tp ny cng c min gi tr kiu boolean. d. Mt tp B = {B1, B2, ... Bk} cc khch hng ang thng lng vi agent bn. Mi khch hng c biu din qua cc thng tin sau: Tp cc n v hng ho b t chi, n v hng ho va mi gii thiu i, cc thuc tnh v gi tr cc thuc tnh yu cu. Khi , hot ng thng lng ca agent bn din ra theo s c m t trong Hnh 2.9. Khi u: sau khi ng k vi h thng, agent bn s chuyn ngay vo trng thi ch ch cc kt ni n t cc agent mua. Ch: ti y, agent bn s ch i cc kt ni n t cc agent mua. Tu thuc vo ni dung thng ip nhn c m agent bn chuyn vo cc trng thi ph hp. Tm kim: l trng thi m agent bn chuyn vo khi nhn c thng ip find. Ti y, n cp nht thm yu cu ca khch hng va nhn c v tin hnh tm kim cc n v hng ho tho mn cc yu cu m n nhn c. Nu khng tm c n v hng no, n s gi i thng ip relax vi mong mun agent bn s nhng b trn thuc tnh no . Nu tm thy, n chn n v hng ho no em li gi tr li ch gi cao nht gii thiu vi agent mua km theo thng ip check. ng thi cp nht n v hng ho mi nht va c gi i cho khch hng tng ng.


47

Hnh 2.9: M hnh chin lc thng lng ca agent bn

Tm li: l trng thi agent bn chuyn vo khi nhn c thng ip refind. Khi , ns tin hnh tm kim theo cc yu cu c do khng c yu cu mi b sung. Nu tm thy cc n v hng ho mi, agent bn s chn n v hng no cho gi tr li ch g i cao nht gi n agent mua vi thng ip check. ng thi cp nht n v hng ho mi nht va c gii thiu. Nu khng tm thy hng ho mi, agent bn chuyn vo trng thi khuyn mi xem c th b sung cc hnh thc khuyn mi hay khng.

Khuyn mi: ti y, agent bn ly li n v hng ho mi nht c gii thiu choagent mua kim tra xem n v hng c hnh thc khuyn mi no khng. Vic ny lun m bo c n v hng gii thiu, v trng thi ny ch c chuyn n sau trng thi tm li, trng thi tm li ch xy ra khi agent bn nhn c thng ip refind, tc l trc agent mua nhn c mt n v hng ho do chnh agent bn ny gii thiu. Nu n v hng ny c km theo khuyn mi, agent bn s gi cc hnh thc khuyn mi ny km theo thng ip recheck. Nu n v hng ny khng c khuyn mi hoc c khuyn mi nhng c gii thiu trc , agent bn s gi thng ip relax , ng thi cp nht n v hng ho ny vo tp cc hng ho b t chi.

Kt thc: l trng thi kt thc cho mt phin thng lng vi agent mua m khngphi kt thc cho bn thn agent bn. Trng thi ny t c khi n nhn c thng ip deal bo chp nhn hoc fail bo tht bi t pha agent mua.

Qu trnh trn c th din ra nhiu ln vi mt hoc nhiu agent mua khc nhau. Khc vi agent mua l s kt thc nhim v sau khi thng lng, agent bn ch kt thc nhim v khi bn ht cc mt hng m n qun l.


48

2.3.3 Chin lc thng lng cho agent mua Trong m hnh thng lng song phng, mi agent mua i din cho mt khch hng, s thng lng vi mt i tc duy nht v do mi agent mua c trang b cc tri thc sau: a. Tp A = {A1, A2, ... An} cc thuc tnh ca hng ho. Trong trng hp nhiu mt hng th mi mt hng s c xem xt vi tp thuc tnh ring ca mt hng . Mi thuc tnh Ai c u tin ui tng ng. Trong trng hp thuc tnh Ai c gi tr khong th mi gi tr (hoc khong con cc gi tr) trong khong c mt mc tho mn ngi dng aij . b. Mi thuc tnh Ai c mt gi tr gi l ngng nhng b ca thuc tnh. Gi tr i ca ngng ny cho bit thuc tnh tng ng c th c nhng b thm nu gi tr tho mn aij ca n cha thp hn . i c. Mt gi tr c gi l ngng chp nhn, c trng cho kh nng chp nhn ca ngi dng. Nu kh nng chp nhn ca ngi dng cng cao th ngng chp nhn c gi tr cng thp. Ngha l mt hng ch c chp nhn nu tho mn tng th ca n khng nh hn ngng ny. Ngng chp nhn c c lng t cc quan trng ui v ngng nhng b ca mi thuc tnh nh sau: i c lng ngng chp nhn trn mi thuc tnh i = O(u i , i ) . Hm O c chn tho mn cc iu kin ca nh ngha 3.4. Kt hp cc gi tr li vi nhau bng ton t OWA. Nhn xt rng, vi i yu cu ca ngi dng th nu c t nht mt thuc tnh khng tho mn th mt hng s khng c chp nhn, ngha l trng hp ny thuc dng t nht mt v dng ton t OWA c p dng l ton t Max. = M (1 ,2 ,...n ) . ax

d. Mt tp D cc cp thuc tnh v gi tr ca cc thuc tnh gi i cho bn agent bn. Ti thi im u, agent mua ch gi i cc yu cu ca cc thuc tnh c u tin cao nht. Sau , trong sut qu trnh thng lng, agent mua s gi thm yu cu ch khi gi tr thuc tnh tng ng khng tho mn yu cu ca n. Do vy, khi c yu cu nhng b t pha agent bn, agent mua ch tin hnh chn la kh nng nhng b trn cc thuc tnh c yu cu lu trong tp D ny.


49

Vi tp cc tri thc ny, qu trnh thng lng ca agent mua din ra theo s c minh ho trong Hnh 2.10.

Hnh 2.10: M hnh chin lc thng lng ca agent mua

Khi u: Trong trng thi khi u ca phin thng lng ny, agent mua tm rathuc tnh c u tin ui cao nht gi i. Trong trng hp c nhiu thuc tnh c u tin ui cao nht, n s gi i ton b cc thuc tnh ny.

Yu cu: Khi mun gi i yu cu v thuc tnh mi hoc gi tr mi cho thuc tnh yu cu, agent mua s chuyn vo trng thi yu cu thc hin vic gi cc yu cu cho pha i tc. ng thi vi vic gi yu cu i, agent mua cn phi cp nht li ni dung cc thuc tnh c gi i (tp D) trong b nh hot ng ca mnh.

Ch: L trng thi agent mua ch i mt thng ip phc p t pha i tc. Khinhn c thng ip phc p, tu thuc vo ni dung ca thng ip m agent mua chuyn vo cc trng thi tng ng.

Kim tra: Khi nhn c thng ip kiu check t pha agent bn th agent muachuyn vo trng thi kim tra. Ti y, n tin hnh kim tra xem c thuc tnh no b vi phm hay khng. Mt thuc tnh b coi l vi phm nu gi tr ca n km hn gi tr yu cu ca thuc tnh ang c lu gi trong b nh ng ca agent mua. Khi nim km hn l tu thuc vo thuc tnh ca i tng. Chng hn, vi thuc tnh gi phng th km hn l khi gi phng ca khch sn nhn c cao hn gi c yu cu.


50

Nu c t nht mt thuc tnh b vi phm, agent mua s chuyn sang trng thi yu cu b sung cc yu cu mi. Trong trng hp ngc li, khng c thuc tnh no b vi phm, n s chuyn vo trng thi chp nhn kim tra xem i tng c th chp nhn c khng; bi v khi khng c thuc tnh no b vi phm th cha th chc chn rng mt hng s c chp nhn bi ngi dng.

Chp nhn: Trong trng hp khng c thuc tnh no b vi phm sau trng thi kim tra hoc nhn c thng ip recheck, agent mua s chuyn vo trng thi chp nhn. Cc bc tin hnh tnh tho mn tng th ca i tng i vi ngi dng, da trn cc k thut c lng m c tin hnh nh sau.

Tnh ph hp tng ng bi ca thuc tnh Ai da vo u tin ui v ph hp ai: bi = G(ui,ai). Trong , ai c c lng m theo phng php hnh thang t gi tr thc ca mt hng so vi cc gii hn ca ngi dng trn thuc tnh tng ng. Hm G c chn tho mn cc iu kin ca nh ngha 2.3. Trong p dng c trnh by chng 5, hm chuyn i ph hp tng ng c s dng l G (u , a) = (a 1)u +1 .

Ton t OWA c p dng tnh tho mn rng buc ca mt hng tcc tho mn rng buc bi trn cc thuc tnh Ai. Nhn xt rng mt mt hng mun tho mn c cc rng buc ca ngi dng th n phi tho mn cc rng buc trn tt c cc thuc tnh; vy ton t OWA c p dng l dng tt c mi, tc l ton t dng Min.

= M (b1 , b2 ,... bn ) . in

Tnh tho mn rng buc ca bn bn: bn bn c th c mt s rngbuc i vi ngi mua, chng hn v tui hay cm mang theo vt nui... Khi , tho mn c tnh l phn b (ph nh m) ca gi tr yu thch ca khch hng v iu kin tng ng ( = a i vi ai l yu thch ca ngi dng,ai [0,1] ).

V d: nu khch sn cm a sc vt vo phng m ngi dng mun a theo sc vt vi mc l 40% (0.4) th tho mn rng buc =0.4 =0.6 .

Tnh tho mn khuyn mi : Vi mi hnh thc khuyn mi, tho mns bng yu thch ca khch hng i vi hnh thc khuyn mi ( i = ai vi ai l yu thch ca ngi dng, ai [0,1] ).


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Nu c nhiu hn mt hnh thc khuyn mi cho cng mt mt hng, cc tho mn i c kt hp vi nhau bi mt php ton i xng hai ngi (k hiu l tho mn iu kin:

)

max{ 1 , 2 } 1 2 1 .Trong p dng chng 5, php ton c s dng l 1 2 = 1 + 2 1 2 .

Tnh kh nng chp nhn mt hng t cc gi tr tho mn yu cu , tho mn rng buc v tho mn khuyn mi : = F ( , , ) . Hm Fc chn tho mn cc iu kin ca nh ngha 2.6. Trong p dng chng 4, hm tnh kh nng chp nhn ca ngi dng c s dng l F ( , , ) = min( , ) ((1 ) + ) . Trong l ton t ng nht vi phn t n v , tho mn cc iu kin ca nh ngha 2.5. Trong p dng chng 4, ton t ng nht c p dng la b = (1 ) ab . (1 ) ab + (1 a )(1 b)

vi l ngng chp nhn ca ngi dng. Sau cc bc ny, nu kh nng chp nhn trng thi kt thc (thnh cng). Nu

ln hn ngng chp nhn th mt

hng c chp nhn v agent mua gi thng ip deal n bn bn v chuyn vo

nh hn th mt hng khng c chp

nhn v agent mua s gi thng ip refind yu cu tm li vi cc yu cu c m khng cn gi thm yu cu b sung.

Nhng b: Khi nhn c thng ip relax t agent bn th agent mua chuyn vo trng thi ny. Ti y, n kim tra xem trong cc thuc tnh gi yu cu, c thuc tnh no cn nhng b c na hay khng, mt thuc tnh c coi l cn nhng b c nu gi tr hin ti ca n vn ln hn ngng nhng b ca thuc tnh . Sau khi kim tra, nu khng c thuc tnh no c th nhng b thm, agent mua s gi thng ip fail v chuyn sang trng thi kt thc (tht bi). Ngc li, nu c thuc tnh cn c th nhng b thm, agent mua s chn ra mt thuc tnh nhng b sao cho gi tr li ch ca mnh b gim i l nh nht. Gia tr li ch b mt c c lng da trn tho mn b gim i i v u tin ui

ca thuc tnh . Hm tnh gi tr li ch b mt c chn tho mn iu kin ca nh ngha 3.4 v c th s dng hm L(u , a ) = ua . Khi , agent mua s tm xem thuc tnh Ai no cho gi tr li nh nht. Gi tr thuc tnh y s c nhng b thm mt mc v agent mua chuyn sang trng thi


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yu cu gi i. Trong trng hp c nhiu hn mt thuc tnh cng t gi tr nh nht, agent mua s chn ngu nhin mt trong s cc thuc tnh ny nhng b.

Nh vy, agent mua c th c hai trng thi kt thc l thnh cng hoc tht bi, vic thnh cng hay tht bi u do bn thn agent ny quyt nh. iu ny l ph hp vi thc t khi qu trnh thng lng kt thc l do ngi mua quyt nh mua hoc khng.

2.4 Kt lunChng ny trnh by mt cch khi qut v tng tc trong h a agent, ngn ng truyn thng dng trong tng tc v mt s m hnh tng tc. Cc kin trc h a agent vi agent trung gian c nghin cu v p dng rng ri trong pht trin cc h dch v thng mi in t. Cho n nay c nhiu m hnh thng lng c a ra, m hnh thng lng song phng da trn rng buc m c trnh by nhm p dng cho pht trin h dch v du lch TraNeS s c trnh by trong Chng 5.

CHNG 3: ONTOLOGY TRONG H A AGENT

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CHNG 3

ONTOLOGY TRONG H A AGENT

Khi nim ontology Biu din ontology Phng php lun xy dng ontology

Ontology l mt thut ng trong trit hc nhm m t bn cht ca s tn ti v c s dng rng ri trong lnh vc tr tu nhn to. Trong h a agent, ontology biu din thng tin v tri thc v min quan tm ca cc agent nhm h tr tng tc. Mi ontology l mt cu trc phn lp cc khi nim (concepts), cc thut ng (term) v cc mi quan h (relations) gia cc khi nim, thut ng . Thng qua ontology, cc agent s hiu c ni dung cc thng ip truyn thng m n nhn c trong qu trnh tng tc. Ni dung chng ny nhm trnh by khi nim ontology, vn biu din ontology, vai tr ca ontology trong tng tc a agent v phng php lun tng qut xy dng ontology.

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3.1 Khi nim Ontology3.1.1 Khi nim Ontology l mt thut ng ca trit hc c s dng mt cch rng ri trong lnh vc tr tu nhn to v c nhiu nh ngha khc nhau v ontology ([1], [4], [15], [17], [20], [36]), trong nh ngha ca T. Gruber l c chp nhn rng ri nht. Theo T. Gruber ([15]), Ontology l mt c t hnh thc v khi nim. Cc yu cu cho biu din ontology l: Cc khi nim c dng trong ontology v cc rng buc gia cc khi nim phi c nh ngha mt cch r rng. Ontology phi l dng thng tin sao cho my c th hiu c. Thng tin biu din trong ontology phi c tnh ph qut ngha l thng tin khng ch cho mt thnh phn m cn c chp nhn bi mt nhm cc thnh phn khc nhau.

C th ni, ontology xc nh tp cc thut ng dng m t v biu din cc khi nim da trn mi quan h qua li (hoc rng buc) gia cc khi nim . Cc khi nim trong ontology gip cho vic dng chung v chia s tri thc gia hai min tri thc khc nhau. Khi s dng trong h a agent, ontology l mt cu trc ng ngha c tham chiu trong qu trnh truyn thng gia cc agent, gip cc agent, vi cc min tri thc quan tm khc nhau, c th hiu nhau trong qu trnh trao i (thng qua vic hiu cc message m n nhn c). minh ho cho nh ngha trn, ta xem xt v d trong Hnh 4.1. Cc khi nim nh UserRequest, HotelRequest, TrainRequest ... c biu din di dng cc nt trong mt th c hng. Mi cnh ca th u c nhn biu din mi quan h gia cc khi nim trong th. y ta c ba mi quan h l SubClassOf (khi nim ny l lp con ca khi nim kia), InstanceOf (khi nim ny l th hin ca khi nim kia) v HasA (khi nim ny c mt thuc tnh l khi nim kia).


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UserRequestSubClassOf HotelRequestHasA Distance HasA StarNumber RoomCost InstanceOf InstanceOf TicketPrice HasA HasA Internet Position

SubClassOf TrainRequestHasA HasA HasA Timelost

Cost

Hnh 3.1: V d v ontology

3.1.2 Ontology v c s tri thc Ontology biu din tri thc ca cc agent ch khng phi v d liu ca mt min no . N cung cp tp cc khi nim biu din tri thc trong min quan tm ca cc agent. Cc agent s thng qua ontology hiu nhau trong qu trnh trao i, tng tc. Gia ontology v c s tri thc cng c s khc bit vai tr ca vic biu din tri thc. Cc c im th hin s khc bit ny bao gm: Ontology hng ti vic m t tri thc nh x hi con ngi. Trong khi c s tri thc hng ti vic c t tri thc cho mt lnh vc c th no m h thng cn gii quyt. Ontology lin quan n tri thc min tnh. C s tri thc biu din cc thng thng tin c th b thay i trong qu trnh suy lun. Do , cc lut v cc c ch suy lun l thnh phn rt quan trng ca c s tri thc. Tri thc biu din trong ontology l khng i trong qu trnh suy lun. Ontology biu din cc khi nim nh cc hnh ng, cc qu trnh, cc ti nguyn, cc khi nim khng b thay i khi c suy lun. Trong khi tri thc biu din trong c s tri thc l cc hot ng c thc hin trong mt h ring bit, cc ti nguyn dng to nn cc sn phm c th no . Nhng tri thc nh vy s b thay i trong qu trnh hot ng ca h thng (khi c suy lun).


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Tri thc trong ontology hng ti vic s dng li v dng chung trong cc trnh ng dng. Mc d ontology hng ti vic miu t cc tri thc c tnh cht tnh nhng n vn ph thuc cht ch vo trnh ng dng. Nu hai trnh ng dng cng chung mt min tri thc nhng nhim v li khc nhau th biu din ontology trong min cho mi ng dng l khc nhau. im ny khc vi c s tri thc v trong c s tri thc, tri thc biu din mt min xc nh l nht qun.

Trong mt h thng gm tp hp nhiu agent, m

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