Principle Based Semantics for HPSG

The paper presents a constraint based semantic formalism for HPSG. The advantages of the formlism are shown with respect to a grammar for a fragment of German that deals with (i) quantifier scope ambiguities triggered by scrambling and/or movement and (ii) ambiguities that arise from the collective/distributive distinction of plural NPs. The syntax-semantics interface directly implements syntactic conditions on quantifier scoping and distributivity. The construction of semantic representations is guided by general principles governing the interaction between syntax and semantics. Each of these principles 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 sentence. 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

Co-Indexing Labelled DRSs to Represent and Reason with Ambiguities

The paper addresses the problem of representing ambiguities in a way that allows for monotonic disambiguation and for direct deductive computation. The paper focuses on an extension of the formalism of underspecified DRSs to ambiguities introduced by plural NPs. It deals with the collective/distributive distinction, and also with generic and cumulative readings. In addition it provides a systematic account for an underspecified treatment of plural pronoun resolution.Comment: gzipped ps-file. To appear in: Stanley Peters, Kees van Deemter (1995): Semantic Ambiguity and Underspecification, CSLI Publications, Stanfor

A Reference Architecture for Natural Language Generation Systems

We present the RAGS (Reference Architecture for Generation Systems) framework: a specification of an abstract Natural Language Generation (NLG) system architecture to support sharing, re-use, comparison and evaluation of NLG technologies. We argue that the evidence from a survey of actual NLG systems calls for a different emphasis in a reference proposal from that seen in similar initiatives in information extraction and multimedia interfaces. We introduce the framework itself, in particular the two-level data model that allows us to support the complex data requirements of NLG systems in a flexible and coherent fashion, and describe our efforts to validate the framework through a range of implementations

Non-Restrictive Relative Clauses in Construction Based HPSG.

Abstract This paper presents an account of English non-restrictive ('appositive') relative clauses (NRCs) in the framework of 'construction based' HPSG. Specifically, it shows how the account of restrictive relative clause constructions presented in Sag (1997) can be extended to provide an account of the syntax and semantics of NRCs and of the main differences between NRCs and restrictive relatives. The analysis reconciles the semantic intuition that NRCs behave like independent clauses with their subordinate syntax. A significant point is that, in contrast with many other approaches, it employs only existing, independently motivated theoretical apparatus, and requires absolutely no new structures, features, or types

Semantic transfer in Verbmobil

This paper is a detailed discussion of semantic transfer in the context of the Verbmobil Machine Translation project. The use of semantic transfer as a translation mechanism is introduced and justified by comparison with alternative approaches. Some criteria for evaluation of transfer frameworks are discussed and a comparison is made of three different approaches to the representation of translation rules or equivalences. This is followed by a discussion of control of application of transfer rules and interaction with a domain description and inference component

Zu einer Semantik für Dialogverstehen und Übersetzung

We extend the means of Discourse Representation Theory (DRT) and suggest representations of dialogues that keep track of the speech acts as events that are connected to each other via temporal relations and that can be qualified by predicates of a speech act typology. The contents of the speech acts are represented as flat, underspecified DRSs that are embedded in the global dialogue representation structure. Underspecified means that scope ambiguities are not resolved and flat means that the lexemes are assigned coarse-grained, ambiguity preserving representations. We develop a description language for the meaning of lexemes that provides guidelines for expanding the terms of the language to representations of different semantic granularity. We define coarse-grained representations of some typical expressions of the description language in terms of feature structures. We show how such representations can be incorporated in HPSG-analyses, how, using the Semantics Principle of HPSG, a compositional semantics for flat and underspecified representations can be defined, and how flat representations can be expanded to deeper representations. We sketch the model theory of flat, underspecified representations, point to some nice properties of the suggested HPSG-analyses for Machine Translation and outline the interplay of textual resolution procedures that seems to be needed for disambiguation in the dialogue context