The dialogue-semantic backbone of theGBAis a theory calledKOS(Ginzburg 1996a, Ginzburg 1996b).4 It evolved out of Ginzburg’s investigation of the semantics of questions (Ginzburg 1995a, Ginzburg 1995b). In this latter theory, questions are not only individuated by their set of full answers, as in more traditional approaches (e.g. (Groenendijk & Stokhof 1997)), but also by their ‘resolvedness condition’, which is an agent-relative pragmatic notion. KOS(or theQUD-model, as it is also called) bases on this treatment of questions a theory of dialogue semantics.
1A textbook introduction toHPSGis (Sag & Wasow 1999), the ‘classic’ presentations are (Pollard & Sag 1987, Pollard &
Sag 1994).
2There is a customary, but sloppy manner of speaking in which the descriptions (or rather, the notation format for descriptions) are also called feature structures. Description and model should however not be confused.
3The idea of using partial descriptions / constraints is what connects this syntactic theory nicely to the semantic technique of underspecification which we will later use.
4Apparently,KOSis not an acronym, just the name for the theory (Ginzburg 1996a).
sign
PHON list(form)
SYNSEM
synsem
LOCAL
loc
CAT
cat
HEAD part-of-speech SUBJ list(synsem) COMP list(synsem) SPR list(synsem)
CONT sem-object STORE set(scope-object)
SLASH set(local) WH set(scope-object) BCKGRND set(fact)
CONTXT
C-INDICES
c-ind
C-SPKR index C-ADDR index U-LOC index
SAL-UTT set(local) MAX-QUD question
Figure 5.1: An excerpt of the specification of the type sign from (Ginzburg & Sag 2001)
The model uses a game metaphor to describe dialogue,5according to which the participants (players) make moves in a game whose public effect is recorded on the gameboard and its private effects on private scorecards.KOScombines this with an information state approach, which emphasises the update effects of utterances on a dialogue context.6 The information state in the theory consists of two attributes, the
‘unpublished mental situation’ (UNPUB-MS) and the ‘dialogue game board’ (DGB):
(165)
UNPUB-MS (goals, beliefs etc.)
DGB
FACTS set(proposition)
QUD question
LATEST-MOVE sign
The field ‘unpublished mental situation’ stores the private intentions and beliefs of the DPrelative to which questions get resolved, while the dialogue game board is a complex attribute with the following sub-attributes:
• FACTS, which is the common ground, a set that collects mutually believed propositions.
• QUD, the questions under discussion, a set consisting of the currently discussable questions, par-tially ordered according to the relation of “conversational precedence”, ‘≺’.
• LATEST-MOVE, which stores the content of the latest move made, e.g. “A asserted that p”.
TheQUD-stack is the most important device, since it determines what can coherently be uttered at any point in a discourse.7 It carries almost all the burden of structuring the discourse. The structure arises on the basis that the question maximal onQUDlicenses only information that stands in a certain relation to the question. This follow-up to the question can be realised as a fragment, in which case theQUD
determines how this fragment is resolved. Before we come to this, however, we have to briefly list in what ways information can stand in a relation to theQUD according toKOS. First, it can beabout the question (roughly speaking, by partially answering it), or the informationdecidesthe question by providing an exhaustive answer, or itresolvesit by providing information that is sufficient, relative to the ‘mental situation’ of theDP, i.e. relative to her goals and beliefs; the last notion thus is context (i.e.
agent)-dependent. Questions can stand in the relationdepends-on, where a question q1depends-onon question q2if everything thatdecidesq1also decides q2. Utterances that stand in one of these relations to theQUDare considered coherent in this theory.
Dialogue is dynamic, and the issue at hand can change during the course of a conversation. This poses
5This metaphor can be traced back to (Wittgenstein 1953/84), via (Lewis 1969, Carlson 1983) inter alia.
6Information-State approaches are described in (Traum, Bos, Cooper, Larsson, Lewin, Matheson & Poesio 1999). Such approaches are related to dynamic semantics, where the notion of update likewise is central ((Kamp 1981, Kamp & Reyle 1993, Groenendijk & Stokhof 1991); see also the introduction below in Section 6.3).
7The idea of using questions to structure discourse is based on (Carlson 1983); similar models have been proposed independ-ently by Klein & von Stutterheim (1987) and Roberts (1996) (who even uses the same name,QUD). For a critical discussion of this way of structuring the discourse context, see (Asher 1998).
the question of how theQUDchanges over time, i.e. how questions are put on and removed from theQUD, and how its partial ordering comes about. A question gets removed fromQUD(QUDgets downdated) when information is provided thatresolvesit; the simplest way to update the structure is simply to ask a question. If a question is asked and accepted for discussion it is put on theQUD. The next example shows two updates and two downdates. The stack-architecture ofQUDensures that A’s first answer is related to the second question, and the second answer to the first—i.e., theQUDstructures the discourse into segments.
(166)
A: Who shall we invite for tomorrow? Q1put onQUD
B: Who will agree to come? Q2put onQUD
A: Joe and Peter and maybe Carl. Q2removed fromQUD
B: I see. Peter then. Q1removed fromQUD
(Ginzburg 1997, p.69)
Now certainly not all exchanges in dialogue follow this question-response model. But sinceQUDis the only structuring device, all moves have to have an influence on it. In this model, assertions also give rise to updates of theQUD.8
An assertion “that p” puts the question “whether p” onQUD. The focus partitioning of the assertion can also trigger further updates, as shown in (167).9
(167) a. BILL likes John.→“Who likes John?” onQUD
b. Bill likes JOHN.→“Who does Bill like?” onQUD
c. Bill LIKES John.→“In what relation does Bill stand to John?” onQUD
These are the questions with whichQUD is automatically updated when an assertion is made. Other questions are concerned with the ‘clarification potential’ of utterances, i.e. the possibilities for clarifica-tion they give rise to. We will discuss this separately below in Secclarifica-tion 5.4.
However, often contributions in a dialogue address issues that have not been explicitly raised, as for example in the short dialogue (168). In such cases coherence is preserved under this approach if the dialogue participant is able to construct a question which is relevant at that point in the dialogue, and then accommodates this question onto theQUD. This operation of accommodation must resort to plans and mental states. So far, however, to our knowledge there exists no detailed theory of how to do this.10
8To our knowledge, so far there is no detailed account of how requests would affect theQUD.
9After (Engdahl, Larsson & Ericsson 2000).
10But cf. the first attempts in this direction developed in theTRINDIproject, e.g. (Cooper, Engdahl, Larsson & Ericsson 2000, p.2). The “as cheap as possible” in (168) would in this approach force a question on the stack which hasn’t been raised explicitly.
Cooper et al. (2000) admit that it is rather unintuitive to consider the offering of additional information as answers to as yet unraised questions, and propose to call this “issues raised” instead of questions. Which issues can be raised presumably has to do with the underlying goals theDPs follow.
(168) A: When do you want to travel?
B: Early April. As cheap as possible.
(Cooper et al. 2000, p.2)
We perceive this need for accommodation as a limitation of the model; in our approach, we would simply analyse the relation between B’s two utterances above as an Elaboration, without the need to construct any questions. While it might be possible to always compute and accommodate questions that encap-sulate the semantics of the rhetorical relations introduced in Chapter 2 (“and then what happened?” for Narration, “why?” for Explanation, etc.), using the same techniques of defeasible reasoning described below in Chapter 8, this step of accommodation of questions then becomes superfluous. Hence, it seems to us that theQUD-model would at least have to be extended with a notion of speech acts / rhetorical relations independent from question-answering. We will return to this issue when we discuss theGBA
in the next section.