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ERIC Number: ED524908
Record Type: Non-Journal
Publication Date: 2010
Pages: 263
Abstractor: As Provided
Reference Count: 0
ISBN: ISBN-978-1-1244-2191-9
Efficient Inference for Trees and Alignments: Modeling Monolingual and Bilingual Syntax with Hard and Soft Constraints and Latent Variables
Smith, David Arthur
ProQuest LLC, Ph.D. Dissertation, The Johns Hopkins University
Much recent work in natural language processing treats linguistic analysis as an inference problem over graphs. This development opens up useful connections between machine learning, graph theory, and linguistics. The first part of this dissertation formulates syntactic dependency parsing as a dynamic Markov random field with the novel ingredient of global constraints. Global constraints are enforced by calling combinatorial optimization algorithms as subroutines during message-passing inference in the graphical model, and these global constraints greatly improve on the accuracy of collections of local constraints. In particular, combinatorial subroutines enforce the constraint that the parser's output must form a tree. This is the first application that uses efficient computation of marginals for combinatorial problems to improve the speed and accuracy of belief propagation. If the dependency tree is projective, the tree constraint exploits the inside-outside algorithm; if non-projective, with discontiguous constituents, it exploits the directed matrix-tree theorem, here newly applied to NLP problems. Even with second-order features or latent variables, which would make exact parsing asymptotically slower or NP-hard, approximate inference with belief propagation is as efficient as a simple edge-factored parser times a constant factor. Furthermore, such features significantly improve parse accuracy over exact first-order methods. Incorporating additional features increases the runtime additively rather than multiplicatively. The second part extends these models to capture correspondences among non-isomorphic structures. When bootstrapping a parser in a low-resource target language by exploiting a parser in a high-resource source language, models that score the alignment and the correspondence of divergent syntactic configurations in translational sentence pairs achieve higher accuracy in parsing the target language. These noisy (quasi-synchronous) mappings have further applications in adapting parsers across domains, in learning features of the syntax-semantics interface, and in question answering, paraphrasing, and information retrieval. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page:]
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Publication Type: Dissertations/Theses - Doctoral Dissertations
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A