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Generating Natural Language Summaries from Multiple On-Line Sources: Language Reuse and Regeneration
The abundance of news wire on the World-Wide Web has resulted in at least four major problems, which seem to present the most interesting challenges to users and researchers alike: size,heterogeneity, change, and conflicting information. Size: several hundred newspapers and news agencies maintain their Web sites with thousands of news stories in each. Heterogeneity: some of the data related to news is in structured format (e.g., tables); more exists in semi-structured format (e.g.,Web pages, encyclopedias, textual databases); while the rest of the data is in textual form (e.g., newswire). Change: most Web sites and certainly all news sources change on a daily basis. Disagreement: different sources present conflicting or at least different views of the same event. We have approached the second, third, and fourth of these four problems from the point of view of text generation. We have developed a system, {\scsummons}, which when coupled with appropriate information extraction technology, generates a specific genre of natural language summaries of a particular event (which we call briefings) in a restricted domain. The briefings are concise, they contain facts from multiple and heterogeneous sources, and incorporate evolving information, highlighting agreements and contradictions among sources on the same topic. We have developed novel techniques and algorithms for combining data from multiple sources at the conceptual level (using natural language understanding), for identifying new information on a given topic; and for presenting the information in natural language form to the user. We named the framework that we have developed for these problems {\em language reuse and regeneration} (LRR). Its novelty lies in the ability to produce text by collating together text already written by humans on the Web. The main features of LRR are: increased robustness through a simplified parsing/generation component, leverage on text already written by humans, and facilities for the inclusion of structured data in computer-generated text. The present thesis contains an introduction to LRR and its use inmulti-document summarization. We have paid special attention to the techniquesfor producing conceptual summaries of multiple sources, to the creation and useof a LRR-based lexicon for text generation, to a methodology used to identifynew and old information in threads of documents, and to the generation offluent natural language text using all the components above. The thesis contains evaluations of the different components of {\sc summons} aswell as certain aspects of LRR as a methodology. A review of the relevantliterature is included as a separate chapter
Comprehensive Review of Opinion Summarization
The abundance of opinions on the web has kindled the study of opinion summarization over the last few years. People have introduced various techniques and paradigms to solving this special task. This survey attempts to systematically investigate the different techniques and approaches used in opinion summarization. We provide a multi-perspective classification of the approaches used and highlight some of the key weaknesses of these approaches. This survey also covers evaluation techniques and data sets used in studying the opinion summarization problem. Finally, we provide insights into some of the challenges that are left to be addressed as this will help set the trend for future research in this area.unpublishednot peer reviewe
Building a Generation Knowledge Source using Internet-Accessible Newswire
In this paper, we describe a method for automatic creation of a knowledge
source for text generation using information extraction over the Internet. We
present a prototype system called PROFILE which uses a client-server
architecture to extract noun-phrase descriptions of entities such as people,
places, and organizations. The system serves two purposes: as an information
extraction tool, it allows users to search for textual descriptions of
entities; as a utility to generate functional descriptions (FD), it is used in
a functional-unification based generation system. We present an evaluation of
the approach and its applications to natural language generation and
summarization.Comment: 8 pages, uses eps
Learning Correlations between Linguistic Indicators and Semantic Constraints: Reuse of Context-Dependent Descriptions of Entities
This paper presents the results of a study on the semantic constraints
imposed on lexical choice by certain contextual indicators. We show how such
indicators are computed and how correlations between them and the choice of a
noun phrase description of a named entity can be automatically established
using supervised learning. Based on this correlation, we have developed a
technique for automatic lexical choice of descriptions of entities in text
generation. We discuss the underlying relationship between the pragmatics of
choosing an appropriate description that serves a specific purpose in the
automatically generated text and the semantics of the description itself. We
present our work in the framework of the more general concept of reuse of
linguistic structures that are automatically extracted from large corpora. We
present a formal evaluation of our approach and we conclude with some thoughts
on potential applications of our method.Comment: 7 pages, uses colacl.sty and acl.bst, uses epsfig. To appear in the
Proceedings of the Joint 17th International Conference on Computational
Linguistics 36th Annual Meeting of the Association for Computational
Linguistics (COLING-ACL'98
LexRank: Graph-based Lexical Centrality as Salience in Text Summarization
We introduce a stochastic graph-based method for computing relative
importance of textual units for Natural Language Processing. We test the
technique on the problem of Text Summarization (TS). Extractive TS relies on
the concept of sentence salience to identify the most important sentences in a
document or set of documents. Salience is typically defined in terms of the
presence of particular important words or in terms of similarity to a centroid
pseudo-sentence. We consider a new approach, LexRank, for computing sentence
importance based on the concept of eigenvector centrality in a graph
representation of sentences. In this model, a connectivity matrix based on
intra-sentence cosine similarity is used as the adjacency matrix of the graph
representation of sentences. Our system, based on LexRank ranked in first place
in more than one task in the recent DUC 2004 evaluation. In this paper we
present a detailed analysis of our approach and apply it to a larger data set
including data from earlier DUC evaluations. We discuss several methods to
compute centrality using the similarity graph. The results show that
degree-based methods (including LexRank) outperform both centroid-based methods
and other systems participating in DUC in most of the cases. Furthermore, the
LexRank with threshold method outperforms the other degree-based techniques
including continuous LexRank. We also show that our approach is quite
insensitive to the noise in the data that may result from an imperfect topical
clustering of documents
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