426 research outputs found
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
Semantic Ambiguity and Perceived Ambiguity
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.Comment: Latex, 47 pages. Uses tree-dvips.sty, lingmacros.sty, fullname.st
Epistemic NP Modifiers
The paper considers participles such as "unknown", "identified" and
"unspecified", which in sentences such as "Solange is staying in an unknown
hotel" have readings equivalent to an indirect question "Solange is staying in
a hotel, and it is not known which hotel it is." We discuss phenomena including
disambiguation of quantifier scope and a restriction on the set of determiners
which allow the reading in question. Epistemic modifiers are analyzed in a DRT
framework with file (information state) discourse referents. The proposed
semantics uses a predication on files and discourse referents which is related
to recent developments in dynamic modal predicate calculus. It is argued that a
compositional DRT semantics must employ a semantic type of discourse referents,
as opposed to just a type of individuals. A connection is developed between the
scope effects of epistemic modifiers and the scope-disambiguating effect of "a
certain".Comment: Final pre-publication version, 27 pages, Postscript. Final version
appears in the proceedings of SALT VI
The Parallel Meaning Bank: Towards a Multilingual Corpus of Translations Annotated with Compositional Meaning Representations
The Parallel Meaning Bank is a corpus of translations annotated with shared,
formal meaning representations comprising over 11 million words divided over
four languages (English, German, Italian, and Dutch). Our approach is based on
cross-lingual projection: automatically produced (and manually corrected)
semantic annotations for English sentences are mapped onto their word-aligned
translations, assuming that the translations are meaning-preserving. The
semantic annotation consists of five main steps: (i) segmentation of the text
in sentences and lexical items; (ii) syntactic parsing with Combinatory
Categorial Grammar; (iii) universal semantic tagging; (iv) symbolization; and
(v) compositional semantic analysis based on Discourse Representation Theory.
These steps are performed using statistical models trained in a semi-supervised
manner. The employed annotation models are all language-neutral. Our first
results are promising.Comment: To appear at EACL 201
Ambiguity and reasoning
In this paper, reasoning with ambiguous representations is explored in a formal way, with ambiguities at the level of propositions in propositional logic and predicate logic, and ambiguous representations of scopings in predicate logic as the main examples. First a version of propositional logic with propositional ambiguities is presented and a sequent axiomatization for it is given. This is then extended to predicate logic. Next, predicate logic with scope ambiguities is introduced and discussed, and again a sequent calculus for it is proposed. The conclusion connects the results to natural language semantics, and briefly compares them with existing logics of ambiguity. An appendix gives completeness proofs for our versions of ambiguous propositional and predicate logic
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The Theory of Correlation Formulas and Their Application to Discourse Coherence
The Winograd Schema Challenge (WSC) was proposed as a measure of machine intelligence. It boils down to anaphora resolution, a task familiar from computational linguistics. Research in linguistics and AI has coalesced around discourse coherence as the critical factor in solving this task, and the process of establishing discourse coherence relies fundamentally on world and commonsense knowledge.
In this thesis, we build on an approach to establishing coherence on the basis of it correlation. The utility of this approach lies in its conceptual clarity and ability to flexibly represent commonsense knowledge. We work to fill some conceptual holes with the Correlation Calculus approach. First, understanding the calculus in a vacuum is not straightfoward unless it has a precise semantics. Second, existing demonstrations of the Correlation Calculus on Winograd Schema Challenge problems have not been linguistically credible.
We hope to ameliorate some---but by no means all---of the outstanding issues with the Correlation Calculus. We do so first by providing a precise semantics of the calculus, which relates our intuitive understanding of correlation with a precise notion involving probabilities. Second, we formulate the establishment of discourse coherence by correlation formulas within the framework of Discourse Representation Theory. This provides a more complete and linguistically credible account of the relationship between the Correlation Calculus, discourse coherence, and Winograd Schema Challenge problems.Computer Science
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