The paper presents a constraint based semantic formalism for HPSG. The syntax-semantics interface directly implements syntactic conditions on quantifier scoping and distributivity. The con- struction of semantic representations is guided' by general principles governing the interaction between syntax and semantics. Each of these princip- les acts as a constraint to narrow down the set of possible interpretations of a sentence. Meanings of ambiguous sentences are represented by single partial representations (so-called U(nderspecified) D(iscourse) R(epresentation) S(tructure)s) to which further constraints can be added monotonically to gain more information about the content of a sent- ence. There is no need to build up a large number of alternative representations of the sentence which are then filtered by subsequent discourse and world knowledge. The advantage of UDRSs is not only that they allow for monotonic incremental interpretation but also that they are equipped with truth conditions and a proof theory that allows for inferences to be drawn directly on structures where quantifier scope is not resolved.

We present an efficient and robust reference resolution algorithm in an end-to-end state-of-the-art information extraction system, which must work with a considerably impoverished syntactic analysis of the input sentences. Considering this disadvantage, the basic setup to collect, filter, then order by salience does remarkably well with third-person pronouns, but needs more semantic and discourse information to improve the treatments of other expression types.

Centering Theory is the best known framework for theorizing about local coherence and salience; however, its claims are articulated in terms of notions which are only partially specified, such as ‘utterance’, ‘realization’, or ‘ranking’. A great deal of research has attempted to arrive at more detailed specifications of these PARAMETERS of the theory; as a result, the claims of Centering can be INSTANTIATED in many different ways. We investigated in a systematic fashion the effect of these different ways of setting the parameters on the theory’s claims. Doing this required, first of all, to clarify what the theory’s claims are (one of our conclusions being that what has become known as ’Constraint 1 ’ is actually a central claim of the theory). Secondly, we had to clearly identify these parametric aspects: e.g., we argue that the notion of ‘pronoun ’ used in Rule 1 should be considered a parameter. Thirdly, we had to find appropriate methods for evaluating these claims. We found that while the theory’s main claim about salience and pronominalization, Rule 1–a preference for pronominalizing the CB–is verified with most instantiations, Constraint 1–a claim about (entity) coherence and CB uniqueness–is much more instantiation-dependent: it is not verified if the parameters are instantiated according to very mainstream views (‘Vanilla instantiation’), it only holds if indirect realization is allowed, and is violated by between 20

this paper I treat conditionals using material implication, ignoring the well-known semantic/pragmatic problems concerning their correct interpretation. Of course, one may doubt whether (7a), which is verified by any situation in which there is one woman who did not come to the party, reflects correctly the wide scope reading of the indefinite in (7). Obviously, this problem is independent of the scope problem of indefinites. For this reason and because antecedents of conditionals are one of the simplest and most striking cases of scope islands, I use such examples freely, counting on the reader to substitute her favorite theory of conditionals for material implication. This claim has been challenged in Farkas (1981), Rooth & Partee (1982:fn.6) and, more recently, in Ruys (1992) and Abusch (1994). These works all show cases where Fodor & Sag's claim is argued to be incorrect. The empirical debate will be reviewed later in this paper (subsection 3.4.2). Ruys and Abusch both conclude that Fodor & Sag's "referential" approach is inadequate. To handle the facts, Ruys proposes an indexing mechanism of indefinites within a DRT-like interpretation of LF. Abusch proposes to enrich DRT with a storage mechanism that changes the syntactic position of the N' predicate (= the restriction of the indefinite) at the representational level. Both Ruys and Abusch therefore accept the assumption of DRT about a distinct syntactic representational level for meaning. This level (sometimes called Logical Form') is additional to the syntactic level that undergoes semantic interpretation (GB's Logical Form, other theories' Surface Structure). Indefinites in Ruys and Abusch's treatments are not quantifiers. Instead, they involve the familiar treatment of DRT using free variables. I henceforth c...

I explore some of the issues that arise when trying to establish a connection between the underspecification hypothesis pursued in the NLP literature and work on ambiguity in semantics and in the psychological literature. A theory of underspecification is developed `from the first principles', i.e., starting from a definition of what it means for a sentence to be semantically ambiguous and from what we know about the way humans deal with ambiguity. An underspecified language is specified as the translation language of a grammar covering sentences that display three classes of semantic ambiguity: lexical ambiguity, scopal ambiguity, and referential ambiguity. The expressions of this language denote sets of senses. A formalization of defeasible reasoning with underspecified representations is presented, based on Default Logic. Some issues to be confronted by such a formalization are discussed. 1 The Combinatorial Explosion Puzzle The alternative syntactic readings of a sen...

Conversations involve all sorts of verbal activities beyond those strictly related to the performance of the task at hand. Among other things, the participants in a conversation have to make sure they both understand what's going on, to manage turn taking, and to keep each other informed about their progress in achieving their task. The participants share information about the status of all of these processes; this suggests that the view of the conversational score they share is rather more complex than assumed in previous accounts. We proposed a preliminary formalization of this more complex view of the conversational score in previous work; in this paper we revise that earlier model, and use our theory of the conversational score to give a partial specification of the effect of the dialogue acts included in the DRI classification.

This paper investigates a new representation format for dynamic discourse in DRT, where contextual dynamics is modeled in terms of update conditions. This new representation format is motivated by the study of context dependence in modal constructions, in particular by serious problems besetting earlier approaches to modality and modal subordination in DRT. We present an alternative DRT analysis that provides a unified analysis of relative modality

Abstract. In this paper the Centering model of anaphora resolution and discourse coherence (Grosz, Joshi and Weinstein, 1983, 1995) is reformulated in terms of Optimality Theory (ot) (Prince and Smolensky 1993). One version of the reformulated model is proven to be descriptively equivalent to an earlier algorithmic statement of Centering due to Brennan, Friedman and Pollard (1987). However, the new model is stated declaratively, and makes clearer the status of the various constraints used in the theory. In the second part of the paper, the model is extended, demonstrating the advantages of the ot reformulation, and capturing formally ideas originally described by Grosz, Joshi and Weinstein. Three new applications of the extended ot Centering model are described: generation of linguistic forms from meanings, the evaluation and optimization of extended texts, and the interpretation of accented pronouns.

In this paper, we describe the Rich Representation Language (RRL) which is used in the NECA system. The NECA system generates interactions between two or more animated characters. The RRL is a formal framework for representing the information that is exchanged at the interfaces between the various NECA system modules.

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