The representation of the speech acts

The knowledge about speech acts and the way they relate to each other is stored in the speech acts library, represented in an action hierarchy based on a formalism similar to that by Kautz (1990). In particular, we set apart the decomposition hierarchy (boxed arcs in the figures) and the generalization-specialization hierarchy (thick arrows). When the decomposition includes a single step, the relation between the two actions is a generation relation (Pollack, 1990). The leaves of the hierarchy, surf-imperative, surf-yn-question, surf-wh-question, surf-assertion correspond to the different syntactic types of sentence, namely imperatives, declaratives and interrogatives (two small portions of the library are reported in Figure 1 and 2. There, the surface types are circled by thick ovals).

The actions of the hierarchy are characterized by the following features:

 

 


: Representation of the ask-if speech-act


• parameters: the parameters of an action include the speaker, the hearer

  and a reference to the speech act. The third parameter has different meanings in the various actions of the speech act library: since the interpretation of surface speech acts starts with the analysis of the linguistic aspects in the input utterances (e.g. the detection of politeness features), the actions related to that phase refer to the semantic representation of the input sentences (e.g. consider ask-if, ..., indirect-req in Figure 1). On the other hand, after considering the linguistic aspects, the analysis goes on taking into account the knowledge about domain actions (in order to relate the speaker's utterance to domain goals). So, the third parameter of actions referring to this phase of the analysis refers to an instance of a domain action involved by the speaker's utterance.

  The domain action is recognized from the semantic representation by a plan recognition phase ( action identification (Carberry, 1990), shown in the figures as act-id).

• preconditions: they represent the presuppositions associated with actions (see Searle's felicity conditions (Searle, 1969)). For example, obtain-info (the action of asking information) has the precondition that the speaker does not know the requested information.

• restrictions: they are included in the wh property of actions and, as for parameters, their meaning varies in the different actions of the speech acts library. In the actions related to the analysis of the linguistic aspects of utterances, they concern the linguistic features present in their propositional content. These features are called by Searle (1969) illocutionary force indicating devices and allow the hearer to identify the kind of speech act. They are, for example, the form of the sentence (declarative, interrogative, imperative), the tense and mood of verbs, the presence of modal verbs ( can, want, ...) and performative verbs ( say, ask, order, ...), or particles like please, clearly, etc. An example of this kind of restriction is can2 feature(sem) in ask-if in Figure 1, which restricts the main verb of the sentence to be the second person of the modal potere (`can'). In some actions referring to the domain actions involved by the input utterances, the restrictions may link the parameters of the actions in the speech acts library with the identified domain actions, or with their parameters. For example, in off-record-req in Figure 1, a restriction forces the agent of the identified domain action to be the hearer; this restriction is important in the definition of off-record-req because, when the restriction is not respected, a different speech-act is being performed (e.g. if the agent coincides with the speaker, we have an act of stating her/his plan).

• communicative effects: the actions of the library produce two types of effects: the first one consists in the communicative intentions of the speaker (e.g. when a request is performed successfully, then the speaker and the hearer share the belief that the speaker intends the hearer to perform an action and intends her/his intention to be a mutual knowledge). The second type of effects is related with the politeness consequences of the use of direct/indirect expressions in communication: for example, the effect of the indirect request ind-req1 is to express that the speaker doesn't want to presuppose any hearer's capability in performing the requested action, so that the negative face of the speaker is not threatened.

The recursiveness of natural language implies that illocutionary force indicating devices can be nested inside each other; so, complex utterances including different speech acts can be built and interpreted in a compositional way. For example, the sentence:

2) Vorrei chiederti se puoi dirmi dove si trova la biblioteca.

[I would like to ask you whether you can tell me where is the library.]

is composed of an external surface statement with conditional mood ( vorrei, ``I would like"), an explicit performative ( chiedere, ``to ask") and an indirect request expressed by an inner yes/no question ( se ..., ``whether ..."). Because of the freedom in the composition of sentences, the speech acts library contains some cyclic paths (see the ask-if action that, in figure 2, occurs in its own definition).