Operational Semantic of an AgentSpeak(L) Interpreter using Late Bindings

Ope a ional Seman ic o an Agen Speak(L) In e p e e Using La e Bindings F an isek Vidensky a, F an isek Zbo il b, Radek Koci cand F an isek V. Zbo il d Depa men o In elligen Sys ems, B no Uni e si y o Technology, Boze echo a 2, B no, Czech Republic Keywo ds: BDI Agen s, Ope a ional Seman ics, Agen Speak(L). Abs ac : Al hough BDI sys ems ha e long been s udied in he ield o agen -based p og amming, he e a e s ill p oblems open o esea ch. One p oblem is ha some pa s o sys ems a e non-de e minis ic in he o iginal speci ica ion. Howe e , inding a sui able de e minis ic me hod can lead o imp o ed a ionali y o an agen ’s beha iou . In ou p e ious wo k, we in oduced la e binding in o he in e p e a ion o Agen Speak(L) language. The main bene i o his app oach is ha he in e p e e chooses subs i u ions only when needed, hus a oiding unnecessa y and inco ec subs i u ion selec ion. In his pape , we p esen a o mal ope a ional seman ics o an in e p e e using la e binding a iables. A well-speci ied ope a ional seman ics is necessa y o he implemen a ion o such an in e p e e and i s u he de elopmen . 1 INTRODUCTION Languages based on BDI pa adigms ha e an im- po an place in p og amming agen s as au onomous p oac i e sys ems. Cu en ly, one o he basic lan- guages is Agen Speak(L) (Rao, 1996) and i s dialec s, such as he ASL language o he Jason sys em (Bo - dini e al., 2007). In he pape (Rao, 1996), whe e he o iginal language was i s in oduced, se e al se- lec ion unc ions we e lis ed ha ul illed hei ole in agen con ol only in he abs ac and in oduced non- de e minism in o agen unc ionali y. In he p ac i- cal easoning phase, hese we e unc ions o selec - ing a goal o ollow and o choosing be ween sui able plans o he selec ed goal. In he execu ion phase, i was a selec ion unc ion o choose an in en ion o be ollowed in a gi en cycle. F om hen o he p esen , a numbe o app oaches ha e been published o ad- d ess hese non-de e minisms o imp o e he a ional- i y o he beha iou o such agen s. Fo example, in (Caillou e al., 2017) he au ho s p esen ed a cogni- i e agen a chi ec u e based on he BDI pa adigm us- ing p io i ies in plan selec ion. In (Nunes and Luck, 2014), so goals we e used o in luence he selec ion o a plan o achie e goals. The au ho s o pape (Wa- ah ps://o cid.o g/0000-0003-1808-441X bh ps://o cid.o g/0000-0001-7861-8220 ch ps://o cid.o g/0000-0003-1313-6946 dh ps://o cid.o g/0000-0002-6965-4104 e s e al., 2015) in oduced wo new app oaches o in en ion selec ion. The same eam o au ho s in he pape (Wa e s e al., 2018) used a pa ial plan ha does no speci y he exac o de o ope a ions in he body o a plan, leading o inc easing he agen ’s lex- ibili y and obus ness. Pape (Yao and Logan, 2016) in oduced he use o he Mon e Ca lo T ee Sea ch me hod o selec in en ion o a oid con lic s in con- cu en ly execu ing plans. One addi ional p oblem ha we belie e has no ecei ed as much a en ion in his sys em has been he choice o subs i u ions du ing bo h phases, i.e., he easoning and execu ion phases. In a simila BDI sys em, dMa s (d’In e no e al., 1997), he need o choose subs i u ions was also men ioned bu also wi hou de ailed me hods o choosing hem. The mo e ad anced CAN (Sa dina and Padgham, 2011) sys em men ions subs i u ions as op ions o choosing plans, which a e chosen i he p e iously chosen plan ins ance (i.e., he plan and any subs i u ions) ails. In his pape , we wan o demons a e he ope a- ional seman ics de ining ansi ion ela ion o in e - p e ing he Agen Speak(L) language using la e bind- ings a iables. We in oduced his app oach in he (Zbo il J e al., 2022) pape . This pape is s uc u ed as ollows. The ollowing sec ion gi es a e y b ie o e iew o Agen Speak(L) and i s cons uc s (such as belie s, goals and plans). Sec ions 3 and 4 will desc ibe he undamen al ope - a ions o la e binding and i s use o in e p e ing an Vidensky, F., Zbo il, F., Koci, R. and V. Zbo il, F. Ope a ional Seman ic o an Agen Speak(L) In e p e e Using La e Bindings. DOI: 10.5220/0011620700003393 In P oceedings o he 15 h In e na ional Con e ence on Agen s and A i icial In elligence (ICAART 2023) - Volume 1, pages 173-180 ISBN: 978-989-758-623-1; ISSN: 2184-433X Copy igh c 2023 by SCITEPRESS – Science and Technology Publica ions, Lda. Unde CC license (CC BY-NC-ND 4.0) 173 agen p og am. We hen p esen he main con ibu ion o his wo k, i.e. he ope a ional seman ics o in e - p e ing he Agen Speak(L) language using la e bind- ing a iables in Sec ion 5. Fu u e wo k is discussed in he las sec ion. 2 AGENT PROGRAM WRITTEN Agen Speak(L) This sec ion will desc ibe he basics o an agen p o- g am w i en in Agen Speak(L). The ollowing ex is based on (Rao, 1996). The essen ial elemen in an agen p og am is he agen , which is de ined as ollows: An agen is gi en by a uple hPB,EQ,BB,AS,IS,Sε,SO,SIi, whe e PB is a plan base, EQ is an e en queue, BB is a belie base, AS is a se o ac ions ha a e execu able by he agen , IS is a se o in en ion s uc u es and Sε,SO,SIa e e en s, op ions and in en ions selec ion unc ions. The pu pose o an agen is o achie e ce ain goals. The e a e wo ypes o goals: achie emen goals and es goals. Goals a e w i en as !g( )and ?g( ) e- spec i ely, whe e gis a p edica e symbol and is a sequence o e ms. Achie emen goals s a e ha he agen wan s o achie e an en i onmen al s a e whe e he a om ep esen ing he goal is ue. The es goal says ha he agen wan s o es whe he he e is uni- ica ion wi h a belie om he base BB, which is a se o belie s in he o m o li e al. Essen ial elemen s o an agen p og am a e plans ha speci y how o achie e a goal. Plans a e w i - en in he o m o e:Ψ←plan. Each plan consis s o he igge ing e en e, con ex condi ions Ψand he body o he plan is composed o a sequence o elemen s ha may be a goal o an ac ion. A igge e en can be in e nal (when a sub-goal needs o be achie ed) o ex e nal ( igge ed when he belie base is upda ed while obse ing he en i onmen ). Gen- e ally, an e en is igge ed by adding (p e ix +) o emo ing (-) a belie o a goal. Fo cla i ica ion, we men ion ha belie s, e en s and goals a e w i en as i s -o de logic a omic o - mulas (a oms). Also, a con ex condi ion o a plan is ei he a omic o mula o a se o a omic o mulas in conjunc ion. In each cycle, an e en is selec ed o p ocessing using he unc ion Sε. This e en is hen uni ied wi h he igge ing e en s o he plans in he plan base PB. Plans whose igge ing e en s a e uni ied a e called ele an plans. Rele an plans, whose con ex condi- ions a e a logical consequence o he belie base, a e called applicable plans. One o he applicable plans is hen selec ed using he unc ion SO. This plan is called a possible means o achie ing he goal. The p oblem ha he sys em using la e a iables binding du ing in e p e a ion sol es is ha he subs i- u ions selec ed in one s ep may no longe be applica- ble in he nex s ep. In ha case, he whole delibe - a ion cycle would ha e o be epea ed, which can be a big p oblem in a e y dynamic en i onmen . Ou p oposed sys em uses delayed selec ion o subs i u- ion un il necessa y o sol e his p oblem. This p in- ciple is called la e bindings. The basic me hods used in his sys em a e desc ibed in he ollowing sec ion. 3 OVERVIEW OF OPERATIONS AND FUNCTIONS FOR LATE BINDINGS As men ioned, in ou p e ious a icle (Zbo il J e al., 2022) we de ined ope a ions and unc ions o la e bindings. Fo he pu pose o comple eness, hey will be e-in oduced and b ie ly desc ibed in his sec ion. Uni ie s and subs i u ions play an essen ial ole in la e bindings, as hey a e c ea ed and hen modi ied in each pa o he agen ’s in e p e a ion cycle. The pu - pose o he basic unc ion is o c ea e se s o uni ie s. We called his unc ion b oad uni ica ion. De ini ion 1. B oad uni ica ion, deno ed as ρU, is o mally de ined as: ρU(p,PS)de == {mgu(p,p0):p0∈PS} maps he a om pand a om p0 om he se o a oms PS o a se o all possible mos gene al uni ie s wi hou a iables enaming. The esul o a b oad uni ica ion is a se o uni ie s, which we call a possible uni ie se (PUS). In he ol- lowing ex , we will use he simpli ied o m ρU o he b oad uni ica ion o he a om pand a se o a oms. De ini ion 2. The ins ance se is deno ed by Iσ. This unc ion maps an a om and a PUS o a se o a oms. This ins ance se is de ined as ollows: Iσ(p,ρU)de == {pσ:σ∈ρU} In o mally, he ins ance se con ains each a om ha is c ea ed a e applying each uni ie om he PUS o an a om. I mus be no ed ha he ins ance se is no he in e se unc ion o he b oad uni ica ion. De ini ion 3. The Sho ing unc ion which we de- no ed ≺, is de ined as ollows: ρU≺pde == {σ:∃σ0(σ0∈ρU,σ⊆σ0, ∀[ /x]∈σ0(x∈Va (p)→[ /x]∈σ))} ICAART 2023 - 15 h In e na ional Con e ence on Agen s and A i icial In elligence 174 The esul ing se con ains such subs i u ions ha sub- s i u e ee a iables om p. The ollowing unc ions and ope a ions a e used o modi y PUSs and play an essen ial ole in la e bind- ings. The i s is he me ging ope a ion. I s pu pose is o c ea e a subs i u ion om wo o he subs i u ions. The ope a ion uni es subs i u ions when each a iable is subs i u ed o he same e m in bo h o hem. I a si ua ion a ises whe e he subs i u ions map he same a iable o wo di e en e ms, he esul o he ope - a ion is an emp y se . De ini ion 4. The me ging ope a ion is deno ed as n and is de ined as ollows: σ1nσ2 de ==    σ1∪σ2i ∀[ 1/x1]∈σ1∀[ 2/x2]∈ σ2(x1=x2→ 1= 2) / 0else Assume ha he me ging subs i u ions uni y wo di e en a oms in wo belie bases. I he esul is a non-emp y se , bo h subs i u ions uni y bo h a oms in o he belie bases. Ne e heless, he e may be an- o he pai o uni ie s o which his ope a ion p o- duces a non-emp y se . To ind such a pai , we de ined he es ic ion ope a o . De ini ion 5. We deno ed he es ic ion ope a o by u, his ope a o is de ined as: ρU1uρU2 de == [ σ1∈ρU1,σ2∈ρU2 σ1nσ2 The esul o his ope a o o wo PUS ρU(p1,BB1)and ρU(p2,BB2)is a se o uni ie s ha con ain all he mos gene al uni ie s ha uni y p1in he belie base BB1and p2in he belie base BB2. To ans e subs i u ions when mo ing om one plan o ano he , we in oduced he PUS in e sec ion unc ion. De ini ion 6. The in e sec ion unc ion deno ed by ∼ o PUS ρUand wo a oms p1and p2is de ined as ollows: p1,ρU∼p2 de == ρU(p2,Iσ(p1,ρU)) 4 LATE BINDINGS IN INTERPRETATION OF Agen Speak(L) The easoning p ocess p oduces subs i u ions ha a e used in plan selec ion. I also c ea es subs i u ions by uni ying a plan’s igge ing e en and con ex condi- ions wi h he selec ed (by he Sεselec ion unc ion) e en o p ocess and he agen ’s belie base. In mos BDI sys ems, subs i u ion mus be se- lec ed immedia ely when a plan is selec ed as a means o achie e a goal. Ne e heless, he la e binding sys- em will keep he subs i u ions sepa a e as a PUS. We call his PUS con ex o he plan. This con- ex changes when he agen pe o ms an ac ion o achie es a goal. The sys em can also assign con ex o e en s. Plans and e en s ha do no ha e a selec ed subs i u ion bu ha e an associa ed con ex a e called weak ins ances o plans and e en s. De ini ion 7. A weak plan ins ance is a iple h e,h,c xi, whe e e is a plan’s igge ing e en , h= h1;h2;...;hmis he plan’s body, and c x is he plan’s con ex . Simila ly, we can de ine a weak e en ins ance. De ini ion 8. A weak e en ins ance is a iple he ,ix,c xi, whe e e is an e en , ix is an iden i ie o he in en ion ha aises he e en (o null in case o an ex e nal e en ) and c x is a con ex . We should no e he e ha in he p e ious pape (Zbo il J e al., 2022), he weak e en ins ance was de ined as a uple, and he iden i ie o he in en- ion was missing. This was o simplici y, as we did no need o dis inguish be ween in e nal and ex e nal e en s. Howe e , his will be necessa y o his pape , as you will see la e . The pu pose o a weak e en ins ance is o ep e- sen an e en ha has a isen du ing he execu ion o a weak plan ins ance. Thus, he con ex o he cu - en ly execu ing plan is used o c ea e his weak e en ins ance. In he ollowing ex , we will use he abb e ia ion WPI o weak plan ins ance and WEI o weak e en ins ance. The las de ini ion in his sec ion will be he de i- ni ion o in en ion. De ini ion 9. The in en ion is a s uc u e con aining WEIs o a plan’s igge ing e en and a s ack o WPI plans. Fo mally, i is de ined as ollows: he ,ix,c xi[h e1,h1,c x1i‡h e2,h2,c x2i‡... ‡h en,hn,c xni| whe e he op o he s ack is on he le . I we need o sho en he in en ion no a ion, we eplace pa o all o he s ack con en s wi h P. So he ,ix,c xi[h en,hn,c xni‡P|is also an in en ion. In his and he p e ious sec ions he undamen als o la e binding ha e been p esen ed, and in he nex sec ion he co e o his pape , ope a ional seman ics, will be desc ibed. Ope a ional Seman ic o an Agen Speak(L) In e p e e Using La e Bindings 175 5 OPERATIONAL SEMANTICS A sys em using la e binding a iables pe o ms a p o- g am w i en in he Agen Speak(L) language and in- e p e s i using weak ins ances. I s unc ioning can be desc ibed by ce ain ansi ion ules ha speci y i s ope a ional seman ic (Plo kin, 1981). This is a common ins umen o p ecise o mal speci ica ion o sys em beha iou based on labelled ansi ion ules which de ine he s eps in which a sys em may e ol e. I has been used many imes in he a ea o agen sys- ems; o example, o Agen Speak(L) in e p e a ion in i s basic e sion (Mo ei a and Bo dini, 2002) as well as in he ex ended e sion wi h speech ac s (Mo - ei a e al., 2003), goal dynamic in CAN (Ha land e al., 2014), e c. Labelled ansi ion ules de ine a ela ion among an agen ’s con igu a ions. De ini ion 10. Agen con igu a ion is a uple hPB,EQ,BB,AS,ISi, whe e PB is a se o plans, EQ is an e en queue ha con ains WEIs, BB is a belie base which consis s o g ound a oms, AS is a se o ac ions, and IS is a se o in en ions. When an agen is execu ed, i ’s unning in a se- quence o con igu a ions om an ini ial con igu a- ion o a inal one. The agen ’s cu en con igu a- ion changes ei he when i does some easoning, o when i execu es a plan. Le he e be a ela ion =⇒ AEX (agen ’s execu ion) ha is composed o wo ela ions =⇒ RSN ( easoning) and =⇒ ACT (ac ing), whe e he i s ela ion ep esen s he change o he agen ’s con igu- a ion du ing i s p ac ical easoning p ocess and he second ela ion ep esen s he agen ’s ac ions. Then we de ine ha =⇒ AEX = ( =⇒ RSN ∪=⇒ ACT ), which means ha he AEX ela ion ep esen s bo h p ac ical ea- soning as well as ac ing. The ansi ion ules o he agen ’s execu ion co e bo h hese ela ions. Recall ha he agen i s looks o a means o a goal e en . The means should be a plan which is ele an o he e en , and i is applica- ble due o an agen ’s belie s abou he cu en en i on- men . In his pape , we do no conside any ad anced easoning abou e en selec ion; we assume ha an e en is selec ed as he i s elemen in he e en queue i he queue is no emp y. I di e s om he o igi- nal in e p e a ion in he way i ecognises applicabil- i y and ele ance. 5.1 Rele an and Applicable Plans Fo comple eness, he e is he de ini ion o a ele an and applicable plan in he sys em. Mo e abou p ac i- cal easoning o weak ins ances can be ound in ou p e ious pape (Zbo il J e al., 2022). Assume ha he e is WEI and a plan p, hen he plan pis ele an o he WEI when he PUS in e sec- ion o i s igge ing e en and he e en wi h con ex c ea e a se con aining a leas one subs i u ion. No e ha his is ue e en i he subs i u ion is an emp y se . Fo mally: De ini ion 11. A plan e :b1∧b2∧... ∧bn← h1;h2;...;hmis ele an o a weak e en ins ance he ,ix,c xiwhen (e ,c x ∼ e)6=/ 0 Fo a ele an plan o be applicable, all i s con ex condi ions mus be sa is ied in he belie base. Mo e conc e ely, i mus be possible o ind a PUS o each con ex condi ion and belie base and hen make he es ic ion be ween hem. De ini ion 12. A plan e :b1∧b2∧... ∧bn← h1;h2;...;hmis applicable in he cu en belie base BB i i is ue ha : ρU(b1,BB)u... uρU(bn,BB)6=/ 0 One plan is hen selec ed om he applicable plans using he selec ion unc ion SO. Any plan ha is ele an and applicable can be conside ed a means o achie e a goal, and he agen may choose i as i s in ended means. I he plan is bo h ele an and applicable, hen he es ic ion o PUSs (con ex s) o bo h WPI and WEI mus be a non-emp y PUS. Using he PUS in e sec ion, we can w i e: c x1= ((e ,c x ∼ e)uρU(b1,BB)u ...uρU(bn,BB)) 6=/ 0 and hen c x1is a con ex o a plan which, oge he wi h he plan’s body h1;h2;...;hm, o ms a new WPI ha can be an in ended means o he WEI. 5.2 T ansi ion Rules In he ollowing ex , we can di ide he p esen ed ules in o h ee g oups o de ine he ela ions men- ioned abo e. The i s g oup de ines he ela ion =⇒ RSN using wo ules. The i s ule (PR −EXTEVT) is used in si u- a ions when he agen deals wi h an ex e nal e en and he second ule (PR −INT EV T ) is o he case o an in e nal e en . Bo h hese ules change he agen ’s e en queue and in en ion s uc u e. Bo h also compu e con ex s o ele an and applicable plans, which can all be an in ended means o he e en . Whe he he e en is in e nal o ex e nal depends on he o m ICAART 2023 - 15 h In e na ional Con e ence on Agen s and A i icial In elligence 176 PR-EXTEVT e=he ,null,c xi ∈ EQ p= e :b1∧...∧bn←h∈PB c x1= ((e ,c x ∼ e),ρU(b1,BB)u...uρU(bn,BB)) 6=/ 0 hPB,EQ,BB,AS,ISi=⇒ RSN hPB,EQ −{e},BB,AS,IS ∪{he ,ix,c xi[h e,h,c x1i]}i PR-INTEVT e=he ,ix,c xi ∈ EQ p= e :b1∧...∧bn←h∈PB c x1= ((e ,c x ∼ e),ρU(b1,BB)u...uρU(bn,BB)) 6=/ 0 hPB,EQ,BB,AS,ISi=⇒ RSN hPB,EQ −{e},BB,AS,(IS −{he 2,ix,c x2}i[P]})∪{he 2,ix,c x2i[h e,h,c x1i‡P|}i EXEC1 i=he ,ix,c xi[h e1,h1,c x1i| ∈ IS1 hEQ1,BB1,AS1,(ix :h1,c x1)i → hEQ2,BB2,AS2,(ix :h2,c x2)i hPB1,EQ1,BB1,AS1,IS1i=⇒ ACT hPB1,EQ2,BB2,AS2,(IS1−{i})∪{he ,ix,c xi[h e1,h2,c x2i|})i EXEC2 i=he ,ix,c xi[h e1,h1,c x1i‡P| ∈ IS1 hEQ1,BB1,AS1,(ix :h1,c x1)i → hEQ2,BB2,AS2,(ix :h2,c x2)i hPB1,EQ1,BB1,AS1,IS1i=⇒ ACT hPB1,EQ2,BB2,AS2,(IS1−{i})∪{he ,ix,c xi[h e1,h2,c x2i‡P|})i CLEARINT1 i=he ,ix,c xi[h e1,null,c x1i| ∈ IS hPB,EQ,BB,AS,ISi=⇒ ACT hPB,EQ,BB,AS,(IS −{i})i CLEARFAIL1 i=he ,ix,c xi[h e1, ail,c x1i| ∈ IS hPB,EQ,BB,AS,ISi=⇒ ACT hPB,EQ ∪{he ,null,c xi},BB,AS,(IS −{i})i o he WEI. When he e is no pa en in en ion men- ioned, be e say i is null, hen a new in en ion s ack is c ea ed and an in ended means is inse ed he e. O he wise, he means a e added o he co esponding in en ion s ack. I all h ee condi ions abo e he line a e sa is ied (null in his ule means ha no in en ion is bound o he e en ), hen WEI eis emo ed om an e en queue EQ and a new in en ion ix is c ea ed. This in- en ion is composed o new WEIs he ,ix,c xiand a plan s ack ha con ains WPI h e,h,c x1i. No e ha e is a igge ing e en o he chosen plan, his i s body, and c x1is he con ex compu ed as was shown in De ini ions 11 and 12. The PR −INT EV T ule is simila o he p e ious one. I di e s only in he o m o he p ocessed WEI. The second g oup o ules de ines he =⇒ ACT ela- ion. A he in en ion le el, he agen s y o execu e one s ep o an in en ion om i s in en ion se ( he in en ion was c ea ed o some WEI he 2,ix,c x2i). The e a e six ules (EXEC1, EXEC2, CLEARINT1, CLEARFAIL1, CLEARINT 2, CLEARFAIL2) ha de- ine how he in en ion can change when he agen pe - o ms he i s i em o i s op-le el plan. These ules a e used in si ua ions when an in en ion s ep inishes ei he success ully o unsuccess ully. I he s ep was success ul, hen he e a e wo sepa a e ules o when i comple es he en i e plan, and o when any ac ions emain in he body o he plan. We mus dis inguish whe he he comple ed plan was a op-le el plan o he in en ion o a sub-plan wi hin he in en ion. All hese ules use one mo e lowe -le el ansi ion ela ion ha de e mines he beha iou o he agen a he plan le el. This ansi ion ela ion is deno ed as →and ep esen s one s ep in he plan execu ion. The ollowing ules ans o m n- uples o he o m hEQ,BB,AS,(ix :h,c x)i, whe e EQ,BB and AS a e he same as in De ini ion 10. Se s PB and IS a e omi - ed and ins ead he e is a sho ed e sion o an in en- ion s ack ha con ains i s iden i ie ix,his he body o i s op-le el plan, and c x is i s con ex . The EXEC1 and EXEC2 ules a e de ined o any non-emp y in en ion s ack wi h a non-emp y plan on op o i . Fu he mo e, he execu ion o a plan is as- Ope a ional Seman ic o an Agen Speak(L) In e p e e Using La e Bindings 177 sumed o lead nei he o an emp y plan no o i s ail- u e. The body o he plan should emain in he in- en ion s ack, bu i s body is always unca ed by one i em. In addi ion, o he pa s wi hin he con igu a ion may also be changed. The i s ule is applicable i he WIP is he only elemen o he in en ion s ack, and he second ule is applicable i he e is mo e han one WIP in he in en- ion s ack. When he agen comple es a sub-plan, he sub- plan is emo ed om he in en ion s ack. A sub-plan is comple ed when he e a e no mo e i ems in he body o he plan, which is ep esen ed by null. Ne e he- less, i he plan is he las plan in he in en ion s ack, hen he agen success ully achie es he op-le el goal and he co esponding plan is also emo ed om he IS. Failu e o comple e he plan will esul in he e- mo al o he co esponding plan, and mo eo e , he WEI mus be pu back in o he EQ. The si ua ion is a li le mo e complica ed when he agen comple es a plan o achie e a goal. Some in- o ma ion should be ansmi ed upwa d o he goal- se ing plan. The jus -comple ed plan con ains a con- ex wi h subs i u ions co esponding o all he goals he agen has achie ed du ing execu ion. The highe -le el plan decla ed he achie emen goal !g( 1)in he cu en con ex c x1. Fo his goal, a plan wi h igge e en +!g( 2)was chosen. Assume ha his plan has been success ully comple ed wi h a con ex c x2. I we c ea e an ins ance se om he igge e en g( 2)o he plan and he con ex c x2, we ge all he goals ha he plan achie ed. Using he in- e sec ion g( 2),c x2∼g( 1),c x1o he achie emen goal g( 1)in he con ex c x1wi h he igge ing e en g( 2)in he con ex c x2we ob ain a new con ex c x3. No e ha he body o he plan in he i s line con- sis s o wo pa s - he abs ac pa deno ed as h1and hen he achie emen goal !g( 1). Only he i s pa o h1 emains a e his s ep. I he plan ails and is no he las plan in he in- en ion s ack, hen he plan is emo ed om he s ack and he highe -le el plan s ill con ains he achie e- men goal. The hi d and inal se o ules de ines he agen ’s beha iou a he plan le el. In he la e binding sys em, he es a ge is he only plan i em ha can ail. Whe he i succeeds de- pends on he esul o he es ic ion o he goal a om, he cu en con ex o he plan, and he cu en s a e o he agen ’s belie base. I he esul is an emp y se , i means ha he plan can con inue o execu e, and he se is he new con ex o he plan. In case he es goal ails, he whole plan ails. An achie emen goal may cause a new weak e en ins ance. I he e is no co esponding WEI in he agen ’s EQ and he in en ion s ack o he WEI does no ye exis , he agen c ea es a new weak e en in- s ance and pu s i in o he agen ’s EQ e en queue. O he wise, he achie emen goal is al eady p ocessed o eady o be p ocessed so he agen igno es i . Thus, i a new WEI is c ea ed, hen i consis s o he achie e- men goal a om, an in en ion iden i ie , and a con ex ha is compu ed om he con ex o he o iginal plan unca ed o he a iables o he achie emen goal. In his case, he achie emen goal is no emo ed om he plan and emains in he body o he plan un il he agen achie es i . CLEARINT2 i=he ,ix,c xi[h e1,!g( 1);h1,c x1i‡h+!g( 2),null,c x2i‡P| ∈ IS c x3=g( 2),c x2∼g( 1),c x1 hPB,EQ,BB,AS,ISi=⇒ ACT hPB,EQ,BB,AS,(IS −{i})∪{he ,ix,c xi[h e1,h1,c x3i‡P|}i CLEARFAIL2 i=he ,ix,c xi[h e1,!g( 1);h1,c x1i‡h e2, ail,c x2i‡P| ∈ IS hPB,EQ,BB,AS,ISi=⇒ ACT hPB,EQ,BB,AS,(IS −{i})∪{he ,ix,c xi[h e1,!g( 1);h1,c x1i‡P|}i TESTG c x1=c x uρU(g( ),BB)6=/ 0 hEQ,BB,AS,(ix :?g( );h,c x)i → hEQ,BB,AS,(ix :h,c x1)i TESTFL c x uρU(g( ),BB) = / 0 hEQ,BB,AS,(ix :?g( );h,c x)i → hEQ,BB,AS,(ix : ail,c x)i ACHIEVEG c x1=c x ≺q( ) h!q( ),ix,c x1i[P|/∈IS h+!q( ),ix,c x1i/∈EQ hEQ,BB,AS,(ix :!q( );h,c x)i → hEQ ∪{h!q( ),ix,c x1i},BB,AS,(ix :!q( );h,c x)i ICAART 2023 - 15 h In e na ional Con e ence on Agen s and A i icial In elligence 178 ADDBB σ∈(c x ≺c( )) hEQ,BB,AS,(ix :+c( );h,c x)i → hEQ ∪{h+c( )σ,ix,c xi},BB ∪{c( )σ},AS,(ix :h,c x u {σ})i DELBB σ∈(c x ≺c( )) hEQ,BB,AS,(ix :−c( );h,c x)i → hEQ ∪{h−c( )σ,ix,c xi},BB {c( )σ},AS,(ix :h,c x u {σ})i EXTACT σ∈(c x ≺c( )) hEQ,BB,AS,(ix :c( );h,c x)i → hEQ,BB,AS ∪{c( )σ},(ix :h,c x u{σ})i The p e ious ules changed he con ex using e- s ic ions and o he unc ions and ope a ions in o- duced in sec ion 3. Ex e nal ac ions, as well as bo h ypes o in e nal ac ions, mus be p ecisely speci ied. In o he wo ds, he agen mus know exac ly wha o do. Fo his eason, he ac ion a om mus be g ound and he agen mus decide which conc e e subs i u ion o subs i u ions o use om he con ex o he plan. This does no mean ha only one se o subs i u ions can emain in he con ex . No e ha he e can be mo e han one se o subs i u ions ha map ee a iables o ac ion a oms o he same e ms. Again, he sho ing unc ion is used use he e, which akes a con ex wi h an ac ion a om and maps hem o one pa icula se o subs i u ions o ha a om. I we use hese subs i- u ions o es ic he con ex o he o iginal plan, we ge a new con ex ha sui s he execu ed ac ion. The ollowing h ee ules ADDBB,DELBB and EXTACT espond o he execu ion o an ac ion du ing he execu ion o a plan. I may be he addi ion o e- mo al o a belie om he belie base. Rules ADDBB and DELBB a e used in hese si ua ions. Simila ly, we can de ine he DELBB ule. In bo h ules, he mos sui able subs i u ion is selec ed i s and he ac ion is emo ed om he body o he cu - en ly execu ing plan. A new WEI is hen pu in o he agen ’s e en queue EQ. The esul o he es ic ion o he con ex o he plan and {σ}is used as he new con ex o he op-le el plan. The subs i u ion σis applied o he belie c( )and he esul is inse ed o emo ed om he belie base BB. The las ule is used when an ex e nal ac ion is pe o med. Also in his ule, he subs i u ion σis chosen and is used o compu e he new con ex . The chosen sub- s i u ion is also applied o he ex e nal e en c( )and he esul is inse ed in o he se o ac ion AS. 6 CONCLUSIONS We conside he ansi ion sys em in oduced in his pape o be a basic o mal speci ica ion o he in e - p e a ion o Agen Speak(L) language using la e bind- ings. Such an in e p e a ion in oduces mo e lexibil- i y in o agen decision-making by p ese ing op ions un il a speci ic decision needs o be made o pe o m an ac ion, compa ed o he o iginal app oaches. This agen does no gi e up op ions o i s u u e ac ions p ema u ely and can co ec i s beha iou du ing he execu ion o each plan acco ding o he cu en si ua- ion o i s cu en belie s abou he s a e o he sys em. Cu en ly, such an in e p e a ion is implemen ed in he sys em we p og am in he PROLOG language. In his sys em, i can also be p ac ically e i ied ha o some agen p og ams in ha language, he agen can deal wi h si ua ions ha ail in sys ems wi h classi- cal in e p e a ion. Howe e , he e a e s ill a ew open a eas, o example, he in en ion selec ion unc ion is no de ined. I s implemen a ion can be done in se - e al ways, so i will be necessa y o design se e al solu ions and compa e hem wi h each o he on a p e- p epa ed se o examples using well-de ined me ics. This will be he di ec ion o ou u u e wo k. ACKNOWLEDGEMENTS This wo k has been suppo ed by he in e nal BUT p ojec FIT-S-20-6427. REFERENCES Bo dini, R. H., H¨ ubne , J. F., and Woold idge, M. (2007). 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ICAART 2023 - 15 h In e na ional Con e ence on Agen s and A i icial In elligence 180