20,039 research outputs found
Unrestricted Bridging Resolution
Anaphora plays a major role in discourse comprehension and accounts for the coherence of a text. In contrast to identity anaphora which indicates that a noun phrase refers back to the same entity introduced by previous descriptions in the discourse, bridging anaphora or associative anaphora links anaphors and antecedents via lexico-semantic, frame or encyclopedic relations.
In recent years, various computational approaches have been developed for bridging resolution. However, most of them only consider antecedent selection, assuming that bridging anaphora recognition has been performed. Moreover, they often focus on subproblems, e.g., only part-of bridging or definite noun phrase anaphora. This thesis addresses the problem of unrestricted bridging resolution, i.e.,
recognizing bridging anaphora and finding links to antecedents where bridging anaphors are not limited to definite noun phrases and semantic relations between
anaphors and their antecedents are not restricted to meronymic relations.
In this thesis, we solve the problem using a two-stage statistical model. Given all mentions in a document, the first stage predicts bridging anaphors by exploring a cascading collective classification model. We cast bridging anaphora recognition as a subtask of learning fine-grained information status (IS). Each mention in a text gets assigned one IS class, bridging being one possible class.
The model combines the binary classifiers for minority categories and a collective classifier for all categories in a cascaded way. It addresses the multi-class
imbalance problem (e.g., the wide variation of bridging anaphora and their relative rarity compared to many other IS classes) within a multi-class setting while
still keeping the strength of the collective classifier by investigating relational autocorrelation among several IS classes. The second stage finds the antecedents
for all predicted bridging anaphors at the same time by exploring a joint inference model. The approach models two mutually supportive tasks (i.e., bridging anaphora resolution and sibling anaphors clustering) jointly, on the basis of the observation that semantically/syntactically related anaphors are likely to be sibling anaphors, and hence share the same antecedent. Both components are based
on rich linguistically-motivated features and discriminatively trained on a corpus (ISNotes) where bridging is reliably annotated. Our approaches achieve substantial improvements over the reimplementations of previous systems for all three tasks, i.e., bridging anaphora recognition, bridging anaphora resolution and full
bridging resolution.
The work is – to our knowledge – the first bridging resolution system that handles the unrestricted phenomenon in a realistic setting. The methods in this dissertation were originally presented in Markert et al. (2012) and Hou et al. (2013a; 2013b; 2014). The thesis gives a detailed exposition, carrying out a thorough corpus analysis of bridging and conducting a detailed comparison of our models to others in the literature, and also presents several extensions of the aforementioned papers
Using the web to resolve coreferent bridging in German newspaper text
We adopt Markert and Nissim (2005)’s approach of using the World Wide Web to resolve cases of coreferent bridging for German and discuss the strength and weaknesses of this approach. As the general approach of using surface patterns to get information on ontological relations between lexical items has only been tried on English, it is also interesting to see whether the approach works for German as well as it does for English and what differences between these languages need to be accounted for. We also present a novel approach for combining several patterns that yields an ensemble that outperforms the best-performing single patterns in terms of both precision and recall
Text as scene: discourse deixis and bridging relations
En este artículo se presenta un nuevo marco, “el texto como escena”, que establece
las bases para la anotación de dos relaciones de correferencia: la deixis discursiva y las
relaciones de bridging. La incorporación de lo que llamamos escenas textuales y contextuales
proporciona unas directrices de anotación más flexibles, que diferencian claramente entre tipos
de categorías generales. Un marco como éste, capaz de tratar la deixis discursiva y las
relaciones de bridging desde una perspectiva común, tiene como objetivo mejorar el bajo grado
de acuerdo entre anotadores obtenido por esquemas de anotación anteriores, que son incapaces
de captar las referencias vagas inherentes a estos dos tipos de relaciones. Las directrices aquí
presentadas completan el esquema de anotación diseñado para enriquecer el corpus español
CESS-ECE con información correferencial y así construir el corpus CESS-Ancora.This paper presents a new framework, “text as scene”, which lays the foundations for
the annotation of two coreferential links: discourse deixis and bridging relations. The
incorporation of what we call textual and contextual scenes provides more flexible annotation
guidelines, broad type categories being clearly differentiated. Such a framework that is capable
of dealing with discourse deixis and bridging relations from a common perspective aims at
improving the poor reliability scores obtained by previous annotation schemes, which fail to
capture the vague references inherent in both these links. The guidelines presented here
complete the annotation scheme designed to enrich the Spanish CESS-ECE corpus with
coreference information, thus building the CESS-Ancora corpus.This paper has been supported by the FPU
grant (AP2006-00994) from the Spanish
Ministry of Education and Science. It is based
on work supported by the CESS-ECE
(HUM2004-21127), Lang2World (TIN2006-
15265-C06-06), and Praxem (HUM2006-
27378-E) projects
A constraint-based approach to noun phrase coreference resolution in German newspaper text
In this paper, we investigate the usefulness of a wide range of features for their usefulness in the resolution of nominal coreference, both as hard constraints (i.e. completely removing elements from the list of possible candidates) as well as soft constraints (where a cumulation of violations of soft constraints will make it less likely that a candidate is chosen as the antecedent). We present a state of the art system based on such constraints and weights estimated with a maximum entropy model, using lexical information to resolve cases of coreferent bridging
Antecedent selection techniques for high-recall roreference resolution
We investigate methods to improve the recall in coreference resolution by also trying to resolve those definite descriptions where no earlier mention of the referent shares the same lexical head (coreferent bridging). The problem, which is notably harder than identifying coreference relations among mentions which have the same lexical head, has been tackled with several rather different approaches, and we attempt to provide a meaningful classification along with a quantitative comparison. Based on the different merits of the methods, we discuss possibilities to improve them and show how they can be effectively combined
Comparing knowledge sources for nominal anaphora resolution
We compare two ways of obtaining lexical knowledge for antecedent selection in other-anaphora
and definite noun phrase coreference. Specifically, we compare an algorithm that relies on links
encoded in the manually created lexical hierarchy WordNet and an algorithm that mines corpora
by means of shallow lexico-semantic patterns. As corpora we use the British National
Corpus (BNC), as well as the Web, which has not been previously used for this task. Our
results show that (a) the knowledge encoded in WordNet is often insufficient, especially for
anaphor-antecedent relations that exploit subjective or context-dependent knowledge; (b) for
other-anaphora, the Web-based method outperforms the WordNet-based method; (c) for definite
NP coreference, the Web-based method yields results comparable to those obtained using
WordNet over the whole dataset and outperforms the WordNet-based method on subsets of the
dataset; (d) in both case studies, the BNC-based method is worse than the other methods because
of data sparseness. Thus, in our studies, the Web-based method alleviated the lexical knowledge
gap often encountered in anaphora resolution, and handled examples with context-dependent relations
between anaphor and antecedent. Because it is inexpensive and needs no hand-modelling
of lexical knowledge, it is a promising knowledge source to integrate in anaphora resolution systems
Magnetic excitations and electronic interactions in SrCuTeO: a spin-1/2 square lattice Heisenberg antiferromagnet
SrCuTeO presents an opportunity for exploring low-dimensional
magnetism on a square lattice of Cu ions. We employ ab initio
multi-reference configuration interaction calculations to unravel the Cu
electronic structure and to evaluate exchange interactions in SrCuTeO.
The latter results are validated by inelastic neutron scattering using linear
spin-wave theory and series-expansion corrections for quantum effects to
extract true coupling parameters. Using this methodology, which is quite
general, we demonstrate that SrCuTeO is an almost realization of a
nearest-neighbor Heisenberg antiferromagnet but with relatively weak coupling
of 7.18(5) meV.Comment: 10 pages, 7 figure
Presuppositions in Context: Constructing Bridges
About the book: The First International and Interdisciplinary Conference on Modelling and Using Context, Rio de Janeiro, January 1997, gave rise to the present book, which contains a selection of the papers presented there, thoroughly refereed and revised. The treatment of contexts as bona fide objects of logical formalisation has gained wide acceptance, following the seminal impetus given by McCarthy in his Turing Award address. The field of natural language offers a particularly rich variety of examples and challenges to researchers concerned with the formal modelling of context, and several chapters in the volume deal with contextualisation in the setting of natural language. Others adopt a purely formal-logical viewpoint, seeking to develop general models of even wider applicability. The 12 chapters are organised in three groups: formalisation of contextual information in natural language understanding and generation, the application of context in mechanised reasoning domains, and novel non-classical logics for contextual application
Multi layer chromosome organization through DNA bending, bridging and extrusion
All living cells have to master the extraordinarily extended and tangly nature of genomic DNA molecules in particular during cell division when sister chromosomes are resolved from one another and confined to opposite halves of a cell. Bacteria have evolved diverse sets of proteins, which collectively ensure the formation of compact and yet highly dynamic nucleoids. Some of these players act locally by changing the path of DNA through the bending of its double helical backbone. Other proteins have wider or even global impact on chromosome organization, for example by interconnecting two distant segments of chromosomal DNA or by actively relocating DNA within a cell. Here, I highlight different modes of chromosome organization in bacteria and on this basis consider models for the function of SMC protein complexes, whose mechanism of action is only poorly understood so far
- …