Guido Boella Dipartimento di Informatica Università di Torino

Guido Boella Dipartimento di Informatica Università di Torino
11/16/2018 Cooperation among agents Multi agent systems Guido Boella Dipartimento di Informatica Università di Torino

Cooperation among agents
11/16/2018 Cooperation among agents Intentional stance According to Dennet, attitudes like belief and desire are folk psychology concepts that can be fruitfully used in explanations of rational human behavior. If you were asked to explain why someone is carrying an umbrella, you may reply that he believes it is going to rain and that he does not want to get wet. For an explanation of behavior it does not matter whether one actually possesses these mental attitudes: we describe the behavior of an affectionate cat or an unwilling screw in terms of mental attitudes. Dennet calls treating a person o artifact as a rational agent the ‘intentional stance’.

11/16/2018 Cooperation among agents

11/16/2018 Cooperation among agents “Here is how it works: first you decide to treat the object whose behavior is to be predicted as a rational agent; then you figure out what beliefs that agent ought to have, given its place in the world and its purpose. Then you figure out what desires it ought to have, on the same considerations, and finally you predict that this rational agent will act to further its goals in the light of its beliefs. A little practical reasoning from the chosen set of beliefs and desires will in most instances yield a decision about what the agent ought to do; that is what you predict the agent will do.”

11/16/2018 Cooperation among agents HUMAN AGENTHOOD Il modello che i bdi agents vogliono imitare e’ il comportamento umano. In particolare il fatto che gli esseri umani siano guidati da tre “attitudini”: BELIEFS, DESIRES AND INTENTIONS CREDENZE, GOAL E INTENZIONI Ambiguo fra il significato di scopo e desiderio.

11/16/2018 Cooperation among agents Metaphor (Lakoff) A B f x f(x) x • y f(x • y) f(y) y f : A  B f(x • y)=f(x) • f(y) < A,• > < B,• >

11/16/2018 Cooperation among agents IntenTionality “Intentionality” significa intenzionalità: capacità di avere rappresentazioni interne del mondo: come è (credenze) come vorremmo che sia (desideri) come vogliamo cambiarlo (intenzioni) come dovrebbe essere (obblighi)

11/16/2018 Cooperation among agents Attenzione! IntenSionalità è una cosa differente: intensionale significa che non vale il test della sostituibilità: 2=4/2=sqrt(4) “Pierino crede che 2 sia la metà di 4” “Pierino crede che 2 sia la radice di 4”

11/16/2018 Cooperation among agents FMRI

Bratman: “What Is Intention?”
11/16/2018 Cooperation among agents Bratman: “What Is Intention?” 2 possibili interpretazioni della parola: Azione: “l’ha ucciso intenzionalmente” Stato mentale: “ho l’intenzione di andare a vedere Titanic” Proprieta’: future directed: *“ho l’intenzione di andare al cinema ieri” stato mentale che influenza il comportamento futuro stabili (“committment”) ma revocabili: non posso prevedere cosa accadra’ in futuro, quindi devo poter cambiare idea.

“Why bother today to have an intention about tomorrow?”
11/16/2018 Cooperation among agents “Why bother today to have an intention about tomorrow?” Perche’ non attendere domani sera prima di formarmi (ora) l’intenzione di andare al cinema? Perche’ sprecare risorse per formarmi delle intenzioni ora, se non so cosa accadra’ domani (ad es. Mi potrebbero invitare a cena)? Soluzione alternativa: utilizzare un pianificatore classico e poi scegliere fra le opzioni che propone

Planning + Practical Reasoning?
11/16/2018 Cooperation among agents Planning + Practical Reasoning? Scelgo un obbiettivo Costruisco un piano completo che lo soddisfi Scelgo fra le alternative tramite “decision theory” (probabilita’ eventi + utility function) Limiti: devo conoscere lo stato del mondo piu’ tempo passo a pianificare e decidere, maggiore e’ la probabilita’ che il mondo cambi ad ogni cambiamento del mondo devo ricominciare da capo

RUOLO DELLE INTENZIONI
11/16/2018 Cooperation among agents RUOLO DELLE INTENZIONI Questi problemi sono dovuti alla “resource boundedness”: il ruolo delle intenzioni e’ di limitare lo spazio di ricerca del planning e quello della scelta fra le opzioni. Per questo motivo le intenzioni: sono future directed e (relativamente) stabili: se stabilisco ora una linea di azione per il futuro, le scelte successive dovranno essere compatibili con questa: limito le opzioni possibili. Se ho l’intenzione di andare domattina a prendere un libro in biblioteca, non prendero’ in considerazione l’azione di andare a giocare a tennis

11/16/2018 Cooperation among agents Riguardano piani parziali: non conoscendo in anticipo come puo’ evolvere il mondo, costruisco dei piani che sono incompleti temporalmente (non stabilisco l’ordinamento completo delle azioni) o strutturalmente (non scelgo come eseguire delle azioni complesse). Esempio: Posso avere l’intenzione di andare a prendere un libro in biblioteca, senza aver necessariamente costruito un piano in tutti i suoi dettagli (posso non aver ancora scelto se andare in macchina o prendere il tram, perche’ non so se ci sara’ sciopero). Costituiscono l’input per ulteriori fasi di pianificazione

11/16/2018 Cooperation among agents INTENZIONI E CREDENZE Intendo solo cio’ che credo possibile (i.e. esiste un piano che ritengo eseguibile) credo che eseguiro’ quello che intendo: se intendo andare al cinema domani, credo che domani saro’ al cinema e non a casa (“conduct coordinating pro-attitude”) la stabilita’ delle intenzioni implica che, se fallisce il mio piano, ne cerchero’ un altro per raggiungere il mio scopo controllo se l’esecuzione di un piano ha avuto successo non intendo quelle che credo essere le conseguenze indesiderate delle mie azioni (problema dei “side effects”)

11/16/2018 Cooperation among agents SIDE EFFECTS Intend(A)  Bel(AB) Intend(B) ? Non voglio essere committed verso B: altrimenti dovrei perseguire B anche se A e’ gia’ realizzato (e quindi le mie credenze erano sbagliate). Esempio: Strategic bomber: Intend(bombardare la fabbrica) ma Bel(bombardare la fabbrica uccidere i bimbi della scuola) Terror bomber: Intend(uccidere i bimbi della scuola)

ARCHITETTURA ASTRATTA
11/16/2018 Cooperation among agents ARCHITETTURA ASTRATTA action Plan library Intentions structured into plans Opportunity analyser means-end reasoning Filtering process option Desires perception Beliefs Deliberation process intentions Reasoner

Cos'è un gruppo di agenti
11/16/2018 Cooperation among agents Cos'è un gruppo di agenti Un insieme di agenti BDI che hanno deciso di operare in maniera coordinata al raggiungimento di un obiettivo (goal) per mezzo di una sequenza di azioni (piano). Ad ogni agente è assegnata la responsabilità di una parte del piano.

I vantaggi della cooperazione fra agenti
11/16/2018 Cooperation among agents I vantaggi della cooperazione fra agenti La cooperazione fra agenti BDI permette: di raggiungere obiettivi altrimenti impossibili di raggiungere i risultati desiderati con una maggiore efficienza

... gli svantaggi della cooperazione
11/16/2018 Cooperation among agents ... gli svantaggi della cooperazione L'interdipendenza fra le azioni dei diversi agenti di un gruppo è più difficile da gestire E' necessario coordinare i diversi compiti tramite mezzi di comunicazione Si rischia di lavorare a vuoto se la coesione del gruppo viene meno (quindi è necessario comunicare anche i cambiamenti di commitment)

11/16/2018 Cooperation among agents Tipi di azioni Sollevare un tavolo Giocare una partita di calcio Preparare una cena Cercare un oggetto (fare qualsiasi cosa che un altro agente possa impedire)

11/16/2018 Cooperation among agents Autonomous agents "...to pose a goal to oneself is something about which no external legislation can interfere...". An agent: "cannot undergo any obligation other than what he gives himself on his own. (...) only by this means it is possible to reconcile this obligation (even if it were an external obligation) with our will". Kant (Die Metaphysik der Sitten, 1794)

Stato dell'arte sulla cooperazione
11/16/2018 Cooperation among agents Stato dell'arte sulla cooperazione Bratman, Castelfranchi Cohen e Levesque (1991): i membri di un gruppo comunicano i cambiamenti di commitment Grosz e Kraus (1996): supporto reciproco fra gli agenti (helpful behaviour)

11/16/2018 Cooperation among agents Bratman His objective is to define the notion of shared cooperative activity in terms of individual mental states and their interrelationship, without resorting to collective form of intentions that go beyond the mind of individuals and without introducing ad hoc mental states characterizing cooperative behaviors A shared intention is not an attitude in the mind of some super-agent consisting literally of some fusion of the two agents.

11/16/2018 Cooperation among agents VS The examples that contrast with this ``broadly individualistic" approach are Searle, 1990 (``collective intentional behavior is a primitive phenomenon"), Tuomela, and Gilbert, 1960 (the cooperating agents form ``a plural subject which is no more reducible“)

11/16/2018 Cooperation among agents Key features Mutual responsiveness: Each participating agent attempts to be responsive to the intentions and actions of the other knowing that the other is attempting to be similarly responsible. Where ``responsiveness" means keeping an eye to the behavior of the other and to act on the expectations that an agent has on the partner's behavior. That is, the agents are ``reactive" to the changes in the environment caused by the acts of the partners.

11/16/2018 Cooperation among agents Key features II Commitment to the joint activity: The participants each have an appropriate commitment (though perhaps for different reasons) to the joint activity, and their mutual responsiveness is in the pursuit of this commitment

11/16/2018 Cooperation among agents Key features III meshing: the subplans of the different agents that aim at performing the joint activity must ``mesh" with each other. If they don't, the agents cannot opt out of the group but must work to achieve a meshing.

11/16/2018 Cooperation among agents Key features IV helpful behavior: the agents provide support to the partner without further incentives. This requirement prevents agents to opt out of the group instead of providing further help. If an agent can provide help without undermining his own contribution to the joint activity, he has to do so without any other request, solicitation or promise of reward by his partners. This new commitment ensures also that the partner who needs help does not give up his commitment because he is despairing to receive support from the others.

11/16/2018 Cooperation among agents Key features V Limits of bargaining: Though we share the intention to paint together we might have conflicting preferences about who scrapes and who paints, or about what color paint to use. Such conflicts call for bargaining in some form – not bargaining about whether to paint together but, rather, bargaining about howwe are to paint together

11/16/2018 Cooperation among agents Key features VI No benevolence: Though we share the intention to paint together we might have conflicting preferences about who scrapes and who paints, or about what color paint to use. Such conflicts call for bargaining in some form – not bargaining about whether to paint together but, rather, bargaining about howwe are to paint together

11/16/2018 Cooperation among agents Delegation In delegation an agent needs or likes an action of another agent and includes the action in his own plan. For delegating, an agent has the following attitudes: he believes that the delegated agent can do and will do the action; he has the goal that the other does the action he relies on the action: he restrains himself from doing it and coordinates his own behavior with the predicted action.

11/16/2018 Cooperation among agents Castelfranchi Goal adoption: social action is more than the mere coordination implicit in predicting the behavior of others. The leap to strong social action is exemplified by the situation in which one helps another agent in reaching his goals since he knows that the other has such a goal and, perhaps the other is dependent on him. an agent considers his addressees as agents having a mental state composed of beliefs and intentions.

Anticipatory coordination
11/16/2018 Cooperation among agents Anticipatory coordination Given the interferences arising from sharing the same environment, Castelfranchi claims that: No agents could really ``plan" (also partially) its behavior in a multi-agent world without some anticipatory coordination. There is a co-evolutionary coupling between planning in a multi-agent world and mind-reading ability. where for mind-reading ability it is intended the understanding of goals and plans of the other.

11/16/2018 Cooperation among agents Different levels literal help: x adopts what y has delegated to him. over-help: x maintains the delegated plan but goes beyond it. critical help: x modifies the plan remaining in the limit of the delegated goal. over-critical help: xgoes beyond the goal and modifies y’s plan. hypercritical help: x adopts goals that y didn't considered but he gives up the delegated goal and plan.

Cohen and Levesque: TEAMWORK
11/16/2018 Cooperation among agents Cohen and Levesque: TEAMWORK Any theory of joint action should indicate when communication is necessary

INTENTIONS FOR MULTIAGENTS
11/16/2018 Cooperation among agents INTENTIONS FOR MULTIAGENTS Se invece di un singolo agente si ha a che fare con un gruppo che deve eseguire un certo compito, e’ necessaria una nuova nozione di intenzione che permetta di coordinare l’attivita’ del gruppo. L’intenzione resta uno stato mentale del singolo agente, ma include delle nuove condizioni. Cosi’ come le azioni sono sempre eseguite da un singolo agente. In particolare, per coordinare un gruppo di agenti e’ necessaria la comunicazione fra loro, in modo che la loro azione non prenda strade divergenti. Non e’ sufficiente avere l’intenzione di eseguire la propria parte del piano e il mutual belief che gli altri hanno tale intenzione.

11/16/2018 Cooperation among agents PERMANENT GOAL Achieavement goal (vs maintaineance): A-Goalx(P)  Goalx(later(P))  Belx(P) Committment (fanatical): goal permanente a certe condizioni P-Goalx(P)  A-Goalx(P)  Belx(P)  before[(Belx(P)  Belx(P)), Goalx(later(P))] Relative committment: P-R-Goalx(P,Q)  A-Goalx(P)  Belx(P)  before[(Belx(P)  Belx(P)  Belx(Q) ),

Esempio del “convoglio” [Cohen & Levesque, 91]
11/16/2018 Cooperation among agents Esempio del “convoglio” [Cohen & Levesque, 91] A non sa la strada per andare a casa ma sa che B per andare a casa propria passa davanti alla sua. A segue B senza dirglielo ma B guida troppo veloce e A si perde. B sa che qualcuno lo seguira’ per andare a casa: pero’, se A si ferma per un guasto B crede che A sia arrivato e accellera. A e B sanno mutualmente: A arriva a casa e si ferma. Credendo che ci sia un guasto B si ferma e aspetta A a meta’ strada capisce dove si trova e da quel punto puo’ procedere da solo: ma B continua voler passare davanti a casa di A e a procedere non troppo forte.

11/16/2018 Cooperation among agents The solution of Cohen and Levesque is to propose a weaker notion of cooperation: after one of the partners has dropped his private intention to do his part in the group, he will adopt the intention to make mutually known the reason why he discharged the intention: either because it is impossible to reach the joint goal or because it has already been achieved. Note that, when an agent does not believe that the goal is achievable, the mutual beliefs of the group do not hold anymore. Anyway, the group will achieve the mutual belief about the impossibility of their action only when the agent communicates his discovery.

11/16/2018 Cooperation among agents JOINT INTENTION Un gruppo di agenti ha un joint persistent goal di ottenere P relativo a Q sse: tutti i membri del gruppo credono che P e’ falso tutti mutualmente credono che tutti hanno P come goal e’ creduto mutualmente che continueranno ad avere un weak achievement goal fino a che non sara’ conoscenza mutua fra loro che P e’ vero o che P e’ impossibile da raggiungere o che Q e’ diventato falso. Weak achievement goal P: Un agente ha il goal P e crede che P e’ falso oppure crede che che P e’ vero, irrilevante o impossibile da raggiungere e ha il goal che tale situazione sia mutua conoscenza di tutti i membri del gruppo.

11/16/2018 Cooperation among agents cosa manca ?

11/16/2018 Cooperation among agents Tambe's STEAM System Tambe: proposes an implemented model of cooperation based on the SOAR architecture which has as basic building blocks the notion of joint intention by Cohen and Levesque and the Shared plan operator of Grosz and Kraus

11/16/2018 Cooperation among agents Tambe Since communication is a significant overhead when many agents work together and it is a risk in hostile environments, it must be tailored to the situation. The selectivity in communication is achieved via a decision-theoretic approach. By introducing the notion of utility, Tambe adapts the prescription of the Cohen and Levesque framework of communication, or, more precisely, the prescription to attain mutual belief.

Shared Plans of Grosz and Kraus
11/16/2018 Cooperation among agents Shared Plans of Grosz and Kraus Their goal is to provide a specification of the mental state of the participants in a collaborative activity that handles complex actions and is comprehensive in its treatment of partiality of belief and intention They define how the ``snapshots" of the agents' mental state should look like from the initial minimal state of having a partial shared plan to the one of having a full one that represents the stopping condition for the planning process.

11/16/2018 Cooperation among agents Partial plan S1 eff B1 B11 B12 S12

11/16/2018 Cooperation among agents Shared plans In order to have a shared plan each agent must have: a mutual belief about a (partial) recipe, individual intentions that its own part of the action be done individual intentions that the collaborators succeed in doing the (identified) constituent subactions individual or collaborative plans for the subactions - collaborative plans for having a full recipe

Intend-that vs Intend-to
11/16/2018 Cooperation among agents Intend-that vs Intend-to Among the most important achievements is the introduction and axiomatization of the notion of intending a state of affairs (intend-that); while the standard notion of intention allows only intending single agent action, by means of intend-that agents are allowed to have an attitude towards actions by intending that a given action is successful; in particular, agents can intend that a certain multi-agent action is executed successfully

11/16/2018 Cooperation among agents Intend-that

11/16/2018 Cooperation among agents Partial Shared Plan

11/16/2018 Cooperation among agents Tuomela “The possibility of ascribing goals, beliefs, and actions to collectives relies on the idea that collectives can be taken to resemble persons. I shall here accept this idea, although the analogy does not go very far (partly because collectives are not capable of performing primary actions but only act via their members and representatives). Following common-sense examples, I will accept [...] that both factual and normative beliefs can be ascribed (somewhat metaphorically) to groups, both formal and informal, structured and unstructured.”

11/16/2018 Cooperation among agents Groups as agents

Costruction of social reality
11/16/2018 Cooperation among agents Costruction of social reality Searle argues that there is a distinction between two types of rules, a distinction which also holds for formal rules like those composing normative systems: Some rules regulate antecedently existing forms of behaviour. For example, the rules of polite table behaviour regulate eating, but eating exists independently of these rules. Some rules, on the other hand, do not merely regulate an antecedently existing activity called playing chess; they, as it were, create the possibility of or define that activity. The activity of playing chess is constituted by action in accordance with these rules. Chess has no existence apart from these rules. The institutions of marriage, money, and promising are like the institutions of baseball and chess in that they are systems of such constitutive rules or conventions

11/16/2018 Cooperation among agents Counts as According to Searle, institutional facts like marriage, money and private property emerge from an independent ontology of ``brute“ natural facts through constitutive rules of the form ``such and such an X counts as Y in context C" where X is any object satisfying certain conditions and Y is a label that qualifies X as being something of an entirely new sort. Examples of constitutive rules are ``X counts as a presiding official in a wedding ceremony", ``this bit of paper counts as a five euro bill" and ``this piece of land counts as somebody's private property".

Guido Boella Dipartimento di Informatica Università di Torino

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Guido Boella Dipartimento di Informatica Università di Torino

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