Questions on Dialogue Act Taxonomies

There is currently a broad interest in dialogue acts and dialogue act taxonomies, and new uses, taxonomies, and standardization efforts continue to be proposed. This paper presents a discussion of issues that must be addressed in order to facilitate the shared understanding and use of taxonomies. The discussion is framed in terms of 20 questions, the answers to which will help make the meanings of taxonomy elements more clear to different communities of users. I I N T R O D U C T I O N When engaging in a study related to dialogue pragmatics, a researcher is confronted with a bewildering range of theories and taxonomies of dialogue acts to choose from. Moreover, specific deficits in any given theory often lead researchers to continue to develop new taxonomies to suit their particular purposes. To some degree, this is to be expected; dialogue act taxonomies can be seen as a kind of language for describing communicative events, and new formal languages (e.g. programming languages like Java) and (at a slower pace) natural languages continue to be created. On the other hand, in both natural and artificial languages, the use of similar signs for different concepts can cause confusion and misunderstanding, often with serious undesirable consequences (e.g. in programming languages, the use of = as an assignment rather than equality operator in a boolean context; or the firing of an American city official for using the word niggardly (of independent Scandinavian origin) because it sounded too similar to an offensive racial epithet euphemistically referred to as 'the N word'. Similar confusions often occur when one researcher tries to interpret the dialogue act taxonomy of another. For example, various conditions are used to characterize a dialogue act labeled as inform, including those listed in (i). 1 By the term dialogue acts, I don't mean to limit discussion to those theories and taxonomies that explicitly use this term. Other terms used for the same general concept include locutionary, illocutionary, and perlocutionary acts (Austin 1962), speech acts (Searle 1969), communicative acts (Allwood 1976; Sadek 1991; Airenti et al. 1993), conversation acts (Traum & Hinkelman 1992), conversational moves (Carletta et al. 1997), and dialogue moves (Cooper et al. 1999). My remarks here are intended to apply to the general phenomenon described by this range of terms. Dialogue acts can perhaps be seen as most generic, at least in the context of a forum on dialogue. 2 Washington DC Public Advocate David Howard, in February 1999. 8 20 Questions on Dialogue Act Taxonomies When one encounters such a label, it is often not clear which subset of the constraints in (i) (or perhaps none of them, when an entirely different formulation is used to define an inform) are meant by the labeler to characterize the labeled utterance. This kind of confusion has led some (e.g. (External Interfaces Working Group 1993; Discourse Resource Initiative 1997; FIPA 1997)) to propose standard theories that could be well defined and understood and used across groups, while others (e.g. Allwood 1977; Cohen & Levesque 1990) prefer to treat dialogue act (i.e. illocutionary force) identification as of only secondary importance, as a derived concept within a more general theory of rational interaction, using other concepts as primitives. (1) a. declarative mood was used b. propositional information was expressed c. new information was expressed d. the addressee came to believe what was expressed e. what was expressed is actually believed by the speaker £ what was expressed is actually true It is hard to dispute the claim that dialogue acts are a useful concept, given the wide variety of uses to which they are put. Some of these uses include: representations of the pragmatic meaning of utterances in dialogue theories (Vanderveken 1991; Bunt 1996; Poesio & Traum 1997, 1998), building blocks for grammars of dialogue (Winograd & Flores 1986; Bilange 1991), labels for corpus annotation (Carletta et al. 1997; Alexandersson et al. 1998), agent communication languages (External Interfaces Working Group 1993; Sidner 1994; FIPA 1997; Singh 1998), object of analysis in dialogue systems (Allen et al. 1996; Bretier & Sadek 1996), and element of a logical theory of rational interaction (Sadek 1991). Despite this popularity of the concept, there are still a number of issues that present significant challenges for creating a taxonomy of dialogue acts that can be understood and used by researchers other than the taxonomy designers. Here I will briefly raise some of the issues that have often caused confusion when interpreting one taxonomy of dialogue acts from within the viewpoint of another. These issues must be addressed in order to have a clearer idea of what one means by saying that a dialogue act occurred, whether the dialogue act taxonomy is meant for labeling a naturally occurring corpus, as part of a formal theory of action, or as a systeminternal representation of the dialogue. Although there are many such issues, I focus here on 20, formulated as questions, in homage to the 3 Here and elsewhere in the paper, examples are meant to be representative rather than exhaustive; there is a large amount of work in some of these areas.