Ideal Cooperation in Dialogues Kristiina Jokinen ATR Interpreting Telecommunications Research Laboratories 2-2 Hikaridai, Seika-cho, Soraku-gun Kyoto 619-02 Japan email:
[email protected]
Abstract The paper presents a model of cooperation in dialogues which emphasizes the role of ethical consideration in the formation and persistence of the agents' intentions. It is argued that the agents' knowledge of the task is not enough for successful communication, but the agents must also consider each other ethically. Their cooperation involves not only benevolent goal adoption but also evaluation of the partner's goal in the communicative context, given the agent's own preferences and the general principles of Ideal Cooperation.
1 Introduction
Cooperativeness is a keyword in describing the characteristics of human-human or human-computer communication. It is used to refer to the participants' ability to collaborate with each other on a given task and to provide informative and helpful contributions in a given context. In this paper cooperation refers to the agents' basic attitude: they are willing to receive, evaluate and react to each other's (communicative) actions. However, cooperation is not just a pre-assigned agent disposition to act in a helpful way, but involves reasoning through which the agent determines how to react in the current context, given the agent's own preferences and the general principles of Ideal Cooperation. As [Galliers, 1989] points out, cooperation also includes the ability to negotiate and resolve con icting goals, and so if the agents are always ready to adopt the partner's goals they are benevolent rather than cooperative. Rational, cooperative agents are capable of resolving con icts, misunderstandings and non-understandings by evaluating their preferences and commitments, and in the context of dialogue systems this means that cooperation must be explicitly modelled. The paper is organised as follows. First we discuss the properties of rational, motivated communication and introduce the notion of Ideal Cooperation. We also compare cooperation and collaboration. Then we present a formalisation of Ideal Cooperation, and nally exemplify the formalisation by a dialogue example.
2
Cooperation and Communication
The agents have several di erent desires, some of which they have chosen as their goals. Some goals require other agents' assistance to be achieved, and some may require collaboration as part of the task itself (lift a heavy item, dance a waltz, play tennis, etc.). The agents are also assumed to have rather sel sh view-points: each agent wants to achieve her own goals rst and in the most appropriate way. However, the basic setting of social interaction requires that the agents' sel sh view-points t together: if the agents are to interact a lot, it is better to cooperate since this pays back best in the long run [Axelrod, 1984]. To achieve their goals, the agents thus construct a mutual context in which other agents can recognize their goals and then, hopefully, provide help or collaborate with them. The main means in the construction of mutual context is rational communication: the agents exchange information on the facts related to their goals, as well as on their attitudes and emotions. The basic requirements for communication must of course be ful lled: the agents are in contact, speak the same language and are capable of perceiving and understanding each other's contributions. The agents must also show some degree of willingness and ability to continue the interaction, to cooperate with each other. They need not fully cooperate all the time, and their cooperation may vary within the same interaction, but if there exists a con ict between the agents which becomes so serious that cooperation becomes impossible, there will be no communication either. According to [Allwood, 1976], agents are engaged in Ideal Cooperation (IC), if they: 1. 2. 3. 4.
voluntarily strive to achieve the same purposes, show cognitive consideration towards each other, show ethical consideration towards each other, trust each other to act according to (1) { (3) unless explicit notice is given that this is not the case.
The rst requirement presupposes that the participants are autonomous agents, not forced to cooperate, and their intentions in regard to the communicative situation overlap. The degree of cooperation thus depends
on the freedom the agents are able to exert in their actions: to comply under a threat is not cooperation. An important point in IC is the ethical consideration which says that it is not enough to know the most ecient way to achieve the goal (cognitive consideration), but the partner is to be treated as a rational motivated agent as well. Ethical consideration obliges the agent not to harm or cause pain to the partner, and so it also accounts for the agents' politeness, indirectness, feedback, extra help, explanations, etc. According to [Allwood, 1976], IC, based on the human ability for rational coordinated interaction, creates social normative obligations which concern the speaker's sincerity, motivation, and consideration. Finally, as long as the agents trust each other to act according to these principles, communication appears cooperative. It is possible that the partner only pretends to act according to the principles, but if the agent believes that the partner behaves in a cooperative way, there is no way to nd out the deception: cooperation is not an absolute concept but subject to individual solipsism.
3 Ideal Cooperation and Collaboration
Cooperation is distinguished from collaboration or teamwork [Levesque et al., 1990], where the agents work together on a joint task and are jointly committed to a common goal. It may be argued that IC mixes collaboration and cooperation (e.g. participants have a joint purpose they both try to achieve), but although the two are closely related, there is a clear distinction between collaboration on a particular task and cooperation that the (collaborating) participants show in their interaction. Collaboration is a type of coordinated activity and requires both collaborative planning and action: beliefs and intentions of the individual agent are extended to cover beliefs and intentions that the agent possesses as a member of a group. The members are jointly committed to bringing about a joint goal within a (partial) SharedPlan which plan then controls and constrains the agent's future behaviour and individual intentions. Cooperation deals with the participants' shared awareness and understanding of what is communicated. It supports the construction of mutual context in which to exchange information and achieve speci c task goals1 . However, the agents need not agree on the task that gave rise to the communication in the rst place, contrary to collaboration where a mutually believed joint goal is a prerequisite. Unless the joint purpose is explicitly given or obvious in the context (as when the agent is asked to provide information, or takes part in planning a joint trip), the agents will construct it in the course of the interaction. The agents can thus attempt to achieve loose and general joint purposes ("let's keep in contact"), in which case their actions are mainly constrained by general social requirements rather than a SharedPlan; yet Cf. [Clark and Wilkes-Gibbs, 1990] who talk about communication as a collaborative process, and [Lochbaum, 1994] who refers to knowledge preconditions and their ful lment. 1
the construction of mutual context in which to keep contact is based on the principles of IC. Hence, although cooperation is important in collaboration, the agents need not collaborate to exhibit cooperation. [Levesque et al., 1990] de ne the joint persistent goal in teamwork analogously to the individual persistent goal, except that the agents have a weak mutual goal to achieve p: if they privately discover that p is done, impossible to achieve or irrelevant, they have to make this mutually known. As pointed out by [Grosz and Kraus, 1995], the agents cannot opt out from their joint commitment without telling so to the partner. This paper argues that the agent's commitment to a joint goal is based on her trying to act according to the principles of Ideal Cooperation. The changed status of the joint goal is made known to the partner because the agent considers this an ethically correct thing to do: she is obliged to communicate the changed status in order to be regarded as a rational and cooperative agent, not because she is committed to the joint goal. If the agent opts to act mendaciously (as if committed to the joint goal but not trying to achieve it), she will not make the changed status known.
4
Formalisation of Ideal Cooperation
We use the formulas (BEL x p) and (GOAL x p) to express that x has a belief p and that x has a goal p. (MB x y p) means that the agents x and y mutually believe p. A persistent goal (PGOAL x p q) is de ned as a goal such that the agent x attempts to bring about p until she believes that p is true, it is impossible to achieve, or the reason q for p has become irrelevant [Cohen and Levesque, 1990]. We also need means to reason about plan recipes2 for collaborative task ful lment. For this, we have adopted explicit predicates from the SharedPlan formalism by [Grosz and Kraus, 1995], and adjusted them to our notation. The act-type (Select Rec x p R c) represents the activity of an individual agent x selecting a (partial) recipe R for the proposition p under the constraints c (we have left out the time parameter as time can be included in the constraints). In the beginning, the formula refers to the initial construction of a recipe to achieve p. Later the constraints include the agent's goals and the mutually believed SharedPlan, and the reasoning is constrained by the agent's commitments to these. The meta-predicate CBA ('can bring about'), (CBA x p R c), represents the agent's knowledge about her ability to achieve p within the recipe R under the constraints c. Grosz and Kraus' meta-predicte BCBA 'believe can bring about' is represented with the help of BEL and CBA: (BEL x (CBA x p R c)). We also introduce the meta-predicate WCBA 'weakly can bring about', (WCBA x p R c) to represent the agent's choices 2
Plan recipe refers to step-wise instructions of how to achieve a goal, while plan refers to the agent's mental state to act according to the recipe [Pollack, 1990].
in selecting the appropriate recipe R for the proposition p, and performing or contracting out each constituent action. Consequently, we can represent Grosz and Kraus' meta-predicte WBCBA ('weakly believe can bring about') with the help of BEL and WCBA: (BEL x (WCBA x p R c). The agent's ability to evaluate alternative recipes is captured in the predicate PREFER. Following [Galliers, 1989], we de ne preference as the agent having the goal that eventually p and not the goal that eventually q, given that she believes either p or q can be true in the future. Ideal Cooperation is now de ned from the point of view of the agent who is going to act next. The agent x is Ideally Cooperative with the partner y on the proposition p within the (partial) recipe R under the constraints c, if the agent has a joint purpose with the partner and there exists a recipe S such that it is obtained by cognitive consideration, it is ethically adequate, and the agent trusts the partner to ideally cooperate on it: (1) (IC x y p R c) =def (JOINTP x y p c) and 9 S ((COGNITIVE x p S R) and (ETHICAL x y S) and (TRUST x x y S q)). The proposition p describes events in the world that are caused by the agents: (DONE x a) or (DONE y a) where a covers both physical action and speech acts3 . R contains the agent's goal as well as the mutually believed recipe built so far, and c represents the constraints in which the joint purpose reasoning takes place (see below). We say that the agents have a SharedPlan S, if they mutually believe that they have the same goal to make the recipe S eventually true: (SharedPlan x y S) =def (MB x y (GOAL x 5S) ^ (GOAL y 5S)).4 4.1
Joint purpose
JOINTP represents the condition that ideally cooperative agents voluntarily try to achieve the same purposes. (2) (JOINTP x y p c) =def ((BEL x (GOAL y 5p)) and (PREFER x p p))) (PGOAL x p c). When the agent recognises the partner's goal that eventually p, and if she prefers this goal to be true rather than not true in the future, she will adopt a persistent goal that p relative to the constraints c. JOINTP resembles COOP-I in [Galliers, 1989] (recognition of the 3 In the latter case the event would be better represented as (SAID x p) or (SAID y p), where SAID is an action predicate for uttering an utterance, and p is the proposition communicated by the partner's utterance. The di erence is not relevant in the discussion below. 4 "Eventually" is formally represented as 5, and 5p is true if sometime in the future p becomes true. 5S where S is a recipe is true if each constituent action will be done in the future: 8 s 2 S ((DONE x s) or (DONE y s)).
partner's goal and deliberation whether to cooperate on it or not), except that the agent's persistent goal exists relative to the communicative context which the agent nds herself in, rather than the partner having the goal. The communicative context, or the constraints c under which the persistent goal holds, consists of the following four contextual parameters: (3) (CONTEXT x y p R) =def (INIT x y p R) and (TOPIC p R) and (GOALS x p R) and (EXPECT x y p R) Initiative: one of the agents initiated the proposition, i.e. given the belief that the partner y has the goal that eventually p, then at least one of the agents is committed to the goal that eventually p, relative to R: (INIT x y p R) =def (BEL x (GOAL y 5p)) ) ((PGOAL x p R)) or (PGOAL y p R))) This is similar to COOP-M in [Galliers, 1989] which concerns two agents cooperating on a goal that both independently possess. However, INIT (and other context parameters) describes the reasons for the agent to adopt this goal, so the partner's goal must be recognised, but there is no need to mutually believe that they both have the same goal. The persistent goals also exist relative to the SharedPlan R, not relative to the partner possessing the goal. Topic: the agents talk coherently, i.e. there is a mutual belief that p is part of R: (TOPIC p R) =def (MB x y (p 2 R)) Unful lled goals: if the agent has other goals with respect to R, the current goal is one of them or one that contributes5 to them. (GOALS x p R) =def 8 r 2 R (GOAL x r) ) ((p = r) or (CONTRIBUTE p r)) Expectations: if the agent believes the partner has other goals with respect to R, the current goal is one of them or one that contributes to them. (EXPECT x y p R) =def 8 r 2 R (BEL x ((GOAL y r) ) ((p = r) or (CONTRIBUTE p r)))) If any of the context parameters is false, the agent has no reason to maintain the persistent goal that p (even though the agent may actually prefer p to p!), and so there is no joint purpose in the current context, and no reason to cooperate either.6 5 CONTRIBUTE is analogous to the Contribute-relation in [Lochbaum, 1994]: it is true of two events (actions) if the rst plays a role in bringing about the second. 6 For instance, the agent may prefer the partner's goal to go sightseeing to her not going sightseeing, but if the agent does not believe sightseeing to be relevant in the communicative context, she will not cooperate on this goal.
4.2
Cognitive consideration
COGNITIVE models the agent's capability to plan actions in a competent and adequate way. It deals with the means-end reasoning of how to accommodate the proposition p in the context of the agent's own goals and the SharedPlan R. (4)
(COGNITIVE x p S R) =def (Select Rec x p S R) and 8 s 2 S (BEL x (WCBA x s S) ).
The agent selects the most adequate and ecient recipe S for p on the basis of her individual commitments and enablements. Since the agent is a competent actor, she must also believe that she can weakly bring about the extended recipe, either by performing the necessary constituent actions herself or contracting them out. We call S an Operationally Appropriate Plan [Jokinen, 1995]. 4.3
Ethical consideration
ETHICAL represents the agent's consideration of the partner's rationality and well-being if the partner accepts an Operationally Appropriate Plan as a new SharedPlan. The agent is obliged to evaluate her sincerity and motivation towards S, as well as her beliefs about the partner's assumed abilities and commitments. The reasoning may require reconsideration of the cognitive constraints. S which is also ethically acceptable is called the Ethically Adequate Plan, and the agent commits herself to making it a part of the SharedPlan. (5)
(ETHICAL x y S) =def (GOAL x (MB x y ((GOAL x 5S)^ (GOAL y 5S))))) ((SINCERE x y S) and (MOTIVATED x y S) and (CONSIDERATE x y S))
The agent's sincerity is de ned with respect to the partner and the recipe that she wants the partner to believe. The agent need not be truthful per se as she may insincerily want the partner to act according to something which is not true. However, if the agent acts sincerely, then whenever her goal is that the partner recognises her goal that eventually S, then the agent cannot have the goal that eventually not S. (6)
(SINCERE x y S) =def (GOAL x (BEL y (GOAL x 5S))) ) (GOAL x 5S)
MOTIVATED models the agent's commitment to SharedPlan S: if she has the goal that eventually S, she adopts a persistent goal that S, given the new communicative context. The context again comprises the four contextual factors, updated according to S and the action chosen to be performed next. (7)
(MOTIVATED x y S) =def
8 s 2S (GOAL x 5S) ) (PGOAL x 5S (CONTEXT x y s S))
CONSIDERATE models the agent's belief about the partner's willingness to act according to the recipe S and her ability to weakly bring about the recipe's selected consituent actions. Thus, the agent believes that whenever she has the goal to do a constituent action of the SharedPlan, the partner prefers this goal, and whenever she has a goal that partner does a constituent action, the partner prefers this goal and is also capable of bringing it about in the SharedPlan context. (8) (CONSIDERATE x y S) =def 8 s 2 S (BEL x (((GOAL x (DONE x s)) ) (PREFER y (DONE x s) (DONE x s))) or ((GOAL x (DONE y s)) ) ((PREFER y (DONE y s) (DONE y s)) and (WCBA y s S ((GOAL x 5S) ^ (GOAL y 5S))))))) 4.4
Mutual trust
Finally, the agents have a mutual belief that they act according to the principles of Ideal Cooperation. The new context q is updated according to the intended new SharedPlan S and the action chosen to be performed next: (CONTEXT x y s S). (9) (TRUST x y S q)) =def (MB x y (IC y x s S q)).
5
Dialogue example
As an illustration of how the IC principles work, consider the following misunderstanding between a clerk and a customer (taken from the ATR travel dialogue corpus). The customer wanted to reserve a single room but the clerk informed her that they have single rooms available only for the beginning of her stay and she should move to a double room for the rest of her stay. The customer accepted this. After discussing other relevant issues, the clerk now wants to con rm the reservation. (1) Clerk :
Okay. So I'd like to con rm your reservation, please. That was a single room. [uh] You're arriving on the tenth of August and departing on the sixteenth. Is that right? (2) Customer:[uh] Well, excuse me. [um] Didn't you tell me that there are no single rooms on the thirteenth, fourteenth, and fteenth? (3) Clerk : Yes, that's right but for reservation purposes, [uh] you're one person, so [uh] you want a single room. Is that right? (4) Customer:[oh] I see, then, it's all right.
The SharedPlan R contains, among others, the constituent actions stay(single,from(Aug10),to(Aug12)) and stay(double,from(Aug13),to(Aug15)).
The clerk's intended SharedPlan for the utterance (1) is:
S= R[f(DONE customer confirm(res(single,arr(Aug10), dep(Aug16))))g,
and his current chosen goal is:
(GOAL clerk 5(DONE customer confirm(res(single, arr(Aug10),dep(Aug16))))).
The customer applies IC. She prefers the clerk's goal to be true rather than not true and adopts the goal under the constraints of the current communicative context. However, cognitively considering the goal she comes to believe that she cannot bring it about as such: the only way the goal can be accommodated in the SharedPlan R is rst to con rm with the clerk whether or not their SharedPlan includes single rooms for August 13-15. If yes, she has been led to believe false things and the SharedPlan must be corrected; if not, she cannot con rm the reservation and accept the clerk's goal in the SharedPlan. The customer has the Operationally Appropriate Plan S1 = R [ f(DONE clerk confirm(stay(single, from(Aug13), to(Aug15))))g which she intendes to share with the clerk. Being sincere, motivated and considerate (believing that the clerk can indeed do the con rmation), she selects her goal as (GOAL customer 5(DONE
presents a formalisation of the principles of Ideal Cooperation, which refers to the agents' basic attitude to continue the interaction, and requires that the agents have a joint purpose, they cognitively and ethically consider their partner, and trust each other to be rational cooperative agents. The use of the principles is exempli ed in a dialogue example dealing with misunderstanding.
and produces the response (2). The clerk is now faced with a situation where his goal is not directly ful lled. Although there is a joint purpose with respect to his intended SharedPlan S (the customer has initiated a goal relative to S, it is thematically related to S, contributes to the clerk's goal and conforms to his expectations about the customer's goals), the customer's response indicates that she has a problem with accepting S as a mutual one. The clerk's cognitive consideration to accommodate the customer's goal to S results in the Operationally Appropriate Plan S2 = R [ f(DONE customer
[Allwood, 1976] J. Allwood.
clerk confirm(stay(single,from(Aug13),to(Aug15))))),
confirm(res(single,from(Aug10),to(Aug16)))), (DONE clerk confirm(stay(single,from(Aug13),to(Aug15))))g,
i.e. for the clerk there is no contradiction between his goal to con rm the reservation and the customer's goal to con rm the single room. As he wants to make S2 a mutual SharedPlan, ethical consideration requires that he also believes that the customer prefers S2 and can bring about the tasks that are subcontracted to her, i.e. she can con rm the reservation. However, the customer did not directly cooperate on the reservation con rmation but initiated a new goal on the single room, so she cannot be able to bring about this goal (the clerk trusts the customer to be a cooperative agent, and so instead of questioning her IC, he thinks his previous beliefs about the agent's abilities were wrong). The clerk is now obliged to alter his Operationally Appropriate Plan S2 so that the customer could bring about the con rmation and accept S2 as a SharedPlan. He adds an explanation to bridge the two goals that look contradictory to the customer: the reservation is made for a single person in a single room, although the actual room that the customer will be staying at is single only for the rst part of her stay. This leads to the clerk's contribution (3). The customer is now able to bring about the con rmation, and the misunderstanding is cleared up.
6 Conclusions The paper has studied the basic assumptions behind formation and persistent of the agents' intentions. It
Acknowledgements
The basis of this research was carried out when the author was a JSPS Research Fellow at Nara Institute of Science and Technology. I am grateful to Prof Yuji Matsumoto for providing an excellent research environment at NAIST, and to Dr Tsuyoshi Morimoto for allowing me to continue the research at ATR.
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