Computer Science
ComputerScience,1970-2008-Computer Science-1996.jsonl.gz.gz
Computer Science
ab5a122fc7b46bffc1d4efc5b68b69b240881a16
Goal Formulation based on Communicative Principles

The paper presents the Constructive Dialogue Model as a new approach to formulate system goals in intelligent dialogue systems. The departure point is in general communicative principles which constrain cooperative and coherent communication. Dialogue participants are engaged in a cooperative task whereby a model of the joint purpose is constructed. Contributions are planned as reactions to the changing context, and no dialogue grammar is needed. Also speech act classification is abandoned, in favour of contextual reasoning and rationality considerations.


Introduction
Two general approaches can be distinguished in dialogue management: the structural approach, which uses a dialogue grammar to capture regularities of the dialogue in terms of exchanges and moves (Bilange, 1992;Cawsey, 1993;Grosz and Sidner, 1986), and the intention-based approach, which classifies the speaker's beliefs and intentions into speech acts, and uses planning operators to describe them (Appel% 1985;Allen and Perrault, 1980;Bunt et al., 1984). Both regard natural language as purposeful behaviour, but differ in how this behaviour is to be described. The former sees dialogues as products and compiles participants' beliefs and intentions into a predefined dialogue structure, whereas the latter focusses on the participants' goals, and hides the structure in the relations between acts which contain appropriately chosen sets of beliefs and intentions as their preconditions and effects.
We will not go into detailed evaluation of the approaches, see e.g. (Jokinen, 1994), but draw attention to three aspects of dialogues which have *I am grateful to Yuji Matsumoto for providing an excellent resem'ch environment during my JSPS Postdoctoral Fellowship, and Graham Wilcock for helpful discussions.
not been properly addressed before, although widely acknowledged in literature, and important in building robust Natural Language interfaces: 1. dialogue is a collaborative process and its structure is recognised by external observation, not prescribed as an internal constraint of dialogue management (Sacks et al., 1974;Clark and Wilkes-Gibbs, 1990), 2. the speakers' beliefs and intentions in a given dialogue situation are various, and cannot all be checked when deciding oil the next response (Cherniak, 1986), 3. communicative acts are part of social activity, constrained by normative obligations of rational agency (Allwood, 1976).
We discuss these aspects from the point of view of cooperative goal formulation and present the Constructive Dialogue Model as a new approach to plan system responses. Our departure point is in general conmmnicative principles which constrain cooperative and coherent communication, and radical steps are taken in two respects: the dialogue grammar is abandoned as an infeasible way to describe dialogues, and also speech act recognition is abandoned as a redundant labelling of intention configurations. The first step means that the structure is not built according to structuring rules, but emerges from local coherence as the dialogue goes on. The second step means that beliefs and intentions are dealt with by reasoning about the utterance context and communicative constraints instead of speech act types. The decision about what to say next falls out as a result of the agent complying with the communicative principles which refer to the agent's rationality, sire cerity, motivation and consideration. Combined with contextual knowledge, they account for the acceptability of different alternative responses.
The paper is organised as follows. The theoretical framework and its formalisation as the Constructive Dialogue Model are discussed in Section 2. Section 3 presents how the system's communicative goal is determined, and Section 4 provides comparision with related work. Finally, conclusions and filture directions are given in Section 5.  (Allwood, 1976) in comimmication: (1) assume a joint l)urpose, (2) show cognitive consideration (epistemic rationality regarding appropriate ways to react) and ethical consideration (intention to react in a way that does not prevent the partner fi'om fiflfilling her goals), and (3) trust, that the partner is acting according to the same principles. Ideal cooperation does not mean that the agents always react in the way the partner intended to evoke, but rather, it sets the normality assumptions for the way the agents would behave if no disturbing factors were present. As (Galliers, 1989) points out, conflict resolution forms an important part of human conmmnication, and if systems are always ready to adopt the user's role, they becolne rigid and unrealistic. However, if the conflict becomes so serious that it makes any cooperation impossible, communication will break down as well. Rational agents thus try to conlnlunicate so as to conforln to the shared assumptions about operationally appropriate and ethically acceptable acts in a given situation (Jokinen, 11995). Empirical dialogue research has emphasised collaborative nature of dialogues (Sacks et al., 1974;Clark and Wilkes-Gibbs, 1990). Also computationally oriented dialogue studies show that the users express themselves vaguely and continue with follow-up questions (Moore and Paris, 1993), and our corpus 1 supports the view that even sin> ple information seeking dialogues resemble negotiations rather than straightforward question-answer sequences. Based on these obeservations and the theoretical assumptions of Ideal Cooperation, we distinguished the main factors in rational, cooperative dialogue management as follows: Surface form Expressive intentions Declarative express a belief: want (Sp ,know(He ,P) ) Interrogative desire for information: want (Sp,know(Sp, P) ) hnperative desire for action: want (Sp,do(ge,P)) Exclamative express action:

want (Sp, do (Sp,P))
whereas the information seeker is not expected to teach the information provider how to look for the information. The roles can be further difl'erentiated with respect to social factors such as acquaintance of the addressee and fornlality of the situation. • Communicative obligations. Social, normative requirements that concern the agent's sincerit'9 (exchange information which is true or for which evidence can be provided), motivation (exchange information which is related to one's goals and strategies), and consideration (exchange information which the. partner is able to deal with). • Task. Gives rise to communication. Task goals are planned to complete a real workt task (rent a car, book ~ flight, repair a pump) but because of uneven distribution of knowledge, the agents usually need to collaborate to achieve the goal, and thus formulate com-,nunicative goals to obtain missing information, el. (Guilm, 1994). B. Commmficative act: • Expressive and evocative attitudes. To distinguish between the effects of an utterance and the intentions behind it, Austin's concept of illocution is split up into two: ezpvession of the speaker's attitude and evocation of a reaction in the partner; perlocution corresponds to what is actually achieved by the act: the evoked respoT~se, cf. (Allwood, 1976). Expression may differ fl'om evocation (irony, indirectness), aud the evoked response fi'om the evocative intentions (the agent requests ilfformation that the partner cannot or does not want to disclose; the agent fa.ils to fi'ighten the partner becmme this has guessed the agent's malicious intentions).

A. Communicative situation: C. Communicative context:
• Role. Characterised by global communica-• Expectations. Evocative intentions put live rights and obligations of the agents. E.g. the information provider is expected to give information which is relevant for the task, 1The corpus was collected by the Wizard-of-Oz technique with users trying to find information on car-[tire companies and restaurants in a particular area, and is reported in (Nivre, 1992). pressure on the agent to react in a particular way. Conventional expectations, carried by the surface form ( Fig. 1), serve as anchoring points in reasoning about the partner's communicative goal (Cohen and Levesque, 1990). Initiatives. If the agent has initiated a con> municative goal, she "has the initiative" and also the right to pursue the goal until it is achieved or not relevant anymore. She also has the right to expect the partner to collaborate or at least not prevent the agent from achieving her goal. • Unfulfilled goals. If the expressive attitudes of the partner's response match the evocative intentions of the agent's contribution, the communicative goal of the agent's contribution is fulfilled. An unfulfilled goal is pushed forward or stored for later processing.
When the agent has the right to take the initiative, a previously unfulfilled goal can be taken up. If the goal is still unfulfilled and relevant, it is resumed, otherwise dropped. • Thematic coherence. A competent agent relates the topic of her contribution to what has been discussed previously or marks an awkward topic shift appropriately; otherwise the agent risks being understood. Thematic relatedness is based on the types of relationships which occur in the domain.

The CDM System
The theoretical framework is formalised as an approach to dialogue management called the Constructive Dialogue Model, CDM (Jokinen, 1994).
In CDM, the dialogue is an instrument to exchange new information on a particular topic to complete a real world task, and it is managed locally by reacting to the changed dialogue context. The task division and information flow in a CDM system 2 is shown in Fig. 2. The dialogue manager operates on the Context Model which is a dynamic knowledge base containing facts about the agents' goals, expressive and evocative attitudes, central concepts (topic), and new information. It also has access to three static knowledge bases: Communicative Principles (knowledge about rational, cooperative communication), Application Model (knowledge about tasks and roles), and World Model (general knowledge about the entities and their relations in the world). 3 Dialogue contributions are constructed in three phases corresponding to the three main processing tasl~s. Analysis of the input message results in the user's communicative goal, and contains four subtasks: determine the explicitness level, interpret the propositional content, check coherence and verify obligations. Evaluation of the user goal concerns an appropriate joint purpose and determines the next system goal. Response specifies the system's communicative goal up to the semantic representation using the same subtasks as analysis but in a reverse order. Evaluation and response form the agent's reaction.
2The prototype is implemented in SICStus Prolog 2.1, running under UNIX TM on a Sun SPARCStation.
3 Linguistic knowledge is encoded in a linguistic lexicon and grammar, and not discussed here.  The Context Model is represented as a partitioned Prolog database and the predicates have an extra argument referring to the contribution whose processing introduced them. In the attitude language the predicates know, want and do represent belief, intention and action, respectively, s refers to the system and u to the user. Communicative Principles are reasoning rules of the fort0: if cntxtFactl .... , cntxtFactN then cntxtFactM+1,...,cntxtYactK.
The World Model uses neo-Davidsonian event representation, and the Application Model provides mappings from World Model concepts to task and role related facts.

3
Cooperative Goal Formulation In CDM, joint purpose represents the communicative strategy that an agent has chosen in a particular situation to collaborate with her partner. It is determined by evaluating the partner's goal with respect to the communicative context: expectations, initiatives, unfulfilled goals and coherence.
Assigning binary values to these aspects, we get 2 4 = 16 joint purposes, summarised in Fig. 3. The The joint purpose describes coinnmnieative intentions in a context where no speaker obligations or considerations hold. In order to attend the requirements of a particular communicative situation, the joint purpose needs to be specified with respect to the agent's role, task and communicative obligations.
Specification of the joint purpose via the Application Model captures the cognitive consider= ation of Ideal Cooperation: the agent plans her response to be operationally appropriate in the current situation. The result is a communicative goal (c-goal), a set of communicative intentions instantiated according to the current task and role.
The c-goal is then filtered through communicative obligations which impleinent the ethical consideration of Ideal Cooperation: the agent's communicative competence shows in the ways she can realise the same c-goal in various situations. Some communicative obligations are listed in Fig. 4.
Sincerity: "do I know this or can provide evidence?" 1. Everything that the speaker asserts or implies is true unless otherwise explicitly stated.
Motivation: "can I say this?" 1. Everything that the speaker wants to know or wants the partner to do is motivated except if the speaker cmmot take the initiative on it. 2. Everything that addresses what the partner wanted to know or wanted the speaker to do is motivated, except if the speaker emmot disclose the information or do the act. 3. Everything that is related to CC is motivated if not already known. 4. Everything that informs of inconsistency is motivated if not already known.
Consideration: "may I say this?" 1. If the partner's goal cammt be fulfilled (presuppositions are false, facts contradictory, no information exists), it is considerate to inform why (explain, compensate, initiate repair). 2. If the response would repeat previous information, it is considerate to leave this implicit unless the information is assigned a special emphasis. 3. If the partner's response is unrelated, it is considerate to inform of the irrelevance, given that the speaker has unfulfilled goals. 4. [f the partner did not request a piece of related information, it is considerate to include this explicitly in the response, given that the speaker intends to close the topic.

Example
Consider the following sample dialogue where tile system's task is to provide service information to the user: Uh I need a car. $1: Do yon want to buy or rent one? Ui: Rent. $2: Where? U3: In Bolton. $3: OK. ttere are the car hire companies in Bolton: ....
The analysis of the first user contribution U1 is given in Fig. 5. The content of the user's c-goal is inferred from the World Model which says that 'needing a car' can be interpreted as 'wanting to have a cl~r'.
NEW INPO: needE(n,u,c), user(u), car(c) USER C-GOAL: want (u, want(s, know(s, [want~e E(h, u, e )]) )) CENTRAL CONCEPT: needE (n,u,c) EXPRESSIVE ATTITUDES: intention: user intend that system know P: want (u, know(s,[needE(n,u, c ), user(u), car(c)])) assumptions: user know that system not know P: know (u, not know(s,[needE(n,u,d, user(u),car(e)])) EVOCATIVE ATTITUDES: intention: user intend that system intend that system know P: want (u, want#, know(s, [.eed E(n, u, c ), user(u ), ear(c)]))) want (u, want(s, know(s,[wantHave E(h,u,c )], user(u ),~a,'(~ )]) ) ) In the beginning of the dialogue the system has no unfulfilled goals, and its role as an obedient information provider does not allow it to have the initiative. Moreover, any contribution is trivially unrelated to the previous topic, since no previous topic exists. According to the Joint Purpose rule (2), the user's c-goal is thus adopted, and the system also takes the initiative, since the user contribution is non-expected (an information seeker is expected to start with a question or a request).
The joint purpose becomes new-indir-request with "user wants to have a car" as the content, i.e. the communicative strategy is to share the user's want to have a car, and check if this want can be satisfied within the Application Model.
The system cannot provide the user with a car, but it can provide information about the services that, enable the user to have a car. Application Model lists car hire companies and car garages as possible services, so the communicative goal is formulated as to know which is the preferred service. The services are associated with renting or buying cars, thus the disjunction is realised as 5'1.
The system responses $2 and 5"3 are based on the same strategy baclcto: the system 'goes back' to adopt the user's previous unfulfilled goal and tries to satisfy this in the updated context. 4 However, they carry different c-goals due to different specification in the Application Model: $2 aims at narrowing down the database search, 5,3 completes the original task. Finally, the communicative obligation Consideration (4) requires that the application service (car hire company) and location (Bolton) are explicitly expressed in $3 before the list of services.
4The user response fulfills expectations and is themaritally related, and the system has the initiative and unfulfilled goals, at least one based on the original task to provide information.

Discussion and related work
In Section 1 we pointed out three important aspects of dialogues which have been insufficiently accounted for in the earlier approaches to dialogue management. In CDM, these aspects form the basis of the system's functionality: dialogues are regarded as collaborative activities, planned locally in the changed context as reactions to the previous contributions and governed by the rationality principles of Ideal Cooperation. The logical omniscience assumption is tackled by partitioning the Context Model and focussing on specific knowledge with the hel f ) of thematic coherence; also rationality considerations constrain reasoning.
By adhering to general communicative principles, CDM provides a new and uniform way to treat various phenomena that have been separately studied in previous research: goal formulation, coherence and cooperativeness. Communicative principles fimetion on the following levels:

Determination of the joint purpose:
reasoning about a communicative strategy in the context (expectations, initiatives, unflflfilled goals, thematic coherence) 2. Selection of the communicative goal: filtering the joint purpose with respect to the agent's role and task. 3. Realisation of the goal: specifying the goal in regard to the communicative obligations sincerity, motivation and consideration.
However, we also use insights from the huge body of research that exists on dialogue management and natural language planning. For instance, the negotiative nature of dialogues is emphasised in (Moore and Paris, 1993) who show how rhetorical knowledge can be combined with the knowledge about the speaker's intentions and communicative goals so that the system can understand follow-up questions or justify its explanations.
Our work differs from this in that we study general requirements of communication rather than rhetorical relations and their augmentation with speaker intentions, to determine @propriate responses. It is possible to modify our joint purpose algorithm with information about rhetorical relations so as to check expectations in regard to argmnentation, or to include rhetorical knowledge in the obligations used when reasoning about multisentential contributions, but as our primary goal has been to specify communicative principles and use them in the formalisation of the cooperative and rational nature of dialogues, this kind of extension is left for future. (Guinn, 1994) presents a model of mixedinitative negotiation as collaborative problem solving. His Missing Axiom approach demonstrates collaboration and communication between two agents wl~o possess complementary knowledge: if the agent's information is not sufficient to allow completion of the proof the agent is set to do, the agent attempts to provide the missing axioms through interaction. This is similar to our basic assumption of how domain tasks give rise to eonlinunication. The differences lie again in our einphasis on 'Rational and Cooperative Communication' as opposed to 'Interaction as a FMlure to Prove'.
In abandoning dialogue grammar and speech act classification, we agree with the common view currently held among researches: dialogue structure is constructed on the basis of the participants' beliefs and intentions, and speech act types are at most convenient abbreviations for a set of attitudes held by the speakers, but do not constitute an explanation of the dialogue (Cohen and Levesque, 1990;Galliers, 1989). We Mso use contextual knowledge extensively, and connect intention-based approaches to practical dialogue management: rationality and cooperation are not only tied to the agent's beliefs and intentions of the desidered next state of the world, but also to the wider social context in which the communication takes place.

Conclusion and future directions
This paper has presented a new way to formulate system goals in intelligent dialogue systems. It advocates a view-point where the system's fnnctionality is iml)roved by relating the dialogue situation to communication in general. The constraints of rational, cooperative communication p,:ovide the framework in which to deal with contributions: communicators have a joint purpose, they obey communicative obligations and they trust that the partner behaves so that these constraints are tifffilled. Dialogues are dynamic constructions, and contributions are locally planned and realised so that the communicative requirements of the dialogue us a whole are respected.
Current interests concern the extension of the communicative principles into different activities and agent roles. This contributes to the generality of the model by spelling out specific requirements of different communicative situations. It also enables us to study strategic planning and how different roles affect the obligations that the agents want to obey (e.g. in conflict situations). Work is now in progress to cover other types of task dialogues, and to enhance the impleinentation.