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Grammatical Inference for Computational Linguistics [Pehme köide]

This book provides a thorough introduction to the subfield of theoretical computer science known as grammatical inference from a computational linguistic perspective. Grammatical inference provides principled methods for developing computationally sound algorithms that learn structure from strings of symbols. The relationship to computational linguistics is natural because many research problems in computational linguistics are learning problems on words, phrases, and sentences: What algorithm can take as input some finite amount of data (for instance a corpus, annotated or otherwise) and output a system that behaves "correctly" on specific tasks Throughout the text, the key concepts of grammatical inference are interleaved with illustrative examples drawn from problems in computational linguistics. Special attention is paid to the notion of "learning bias." In the context of computational linguistics, such bias can be thought to reflect common (ideally universal) properties of natural languages. This bias can be incorporated either by identifying a learnable class of languages which contains the language to be learned or by using particular strategies for optimizing parameter values. Examples are drawn largely from two linguistic domains (phonology and syntax) which span major regions of the Chomsky Hierarchy (from regular to context-sensitive classes). The conclusion summarizes the major lessons and open questions that grammatical inference brings to computational linguistics.
List of Figures
xv
List of Tables
xvii
Preface xix
1 Studying Learning
1(20)
1.1 An Overview of Grammatical Inference
2(1)
1.2 Formal and Empirical Grammatical Inference
3(2)
1.3 Formal Grammatical Inference
5(5)
1.3.1 Language and Grammar
6(2)
1.3.2 Language Families
8(1)
1.3.3 Learning Languages Efficiently
9(1)
1.4 Empirical Grammatical Inference
10(3)
1.4.1 Languages, Grammars, and Language Families
11(1)
1.4.2 Evaluation
12(1)
1.5 Summary
13(1)
1.6 Formal Preliminaries
14(7)
2 Formal Learning
21(30)
2.1 Introduction
21(3)
2.1.1 The Issues of Learning
21(1)
2.1.2 Learning Scenarios
22(1)
2.1.3 Learning Grammars of Languages
23(1)
2.2 Learnability: Definitions and Paradigms
24(7)
2.2.1 Blame the Data, Not the Algorithm
24(1)
2.2.2 A Non-Probabilistic Setting: Identification in the Limit
24(1)
2.2.3 An Active Learning Setting
25(1)
2.2.4 Introducing Complexity
26(2)
2.2.5 A Probabilistic Version of Identification in the Limit
28(1)
2.2.6 Probably Approximately Correct (PAC) Learning
28(3)
2.3 Grammar Formalisms
31(16)
2.3.1 Finite-State Machines Recognizing Strings
31(3)
2.3.2 Probabilistic Finite-State Machines
34(3)
2.3.3 Transducers
37(4)
2.3.4 More Complex Formalisms
41(5)
2.3.5 Dealing with Trees and Graphs
46(1)
2.4 Is Grammatical Inference an Instance of Machine Learning?
47(2)
2.5 Summary
49(2)
3 Learning Regular Languages
51(34)
3.1 Introduction
51(1)
3.2 Bias Selection Reduces the Problem Space
52(1)
3.3 Regular Grammars
53(3)
3.4 State-Merging Algorithms
56(8)
3.4.1 The Problem of Learning Stress Patterns
56(3)
3.4.2 Merging States
59(1)
3.4.3 Finite-State Representations of Finite Samples
60(2)
3.4.4 The State-Merging Theorem
62(2)
3.5 State-Merging as a Learning Bias
64(2)
3.6 State-Merging as Inference Rules
66(1)
3.7 RPNI
67(2)
3.7.1 How It Works
67(1)
3.7.2 Theoretical Results
68(1)
3.8 Regular Relations
69(2)
3.9 Learning Stochastic Regular Languages
71(10)
3.9.1 Stochastic Languages
72(1)
3.9.2 Structure of the Class Is Deterministic and Known A Priori
73(5)
3.9.3 Structure of the Class Is Deterministic but Not Known A Priori
78(2)
3.9.4 Structure of the Class Is Non-Deterministic and Not Known A Priori
80(1)
3.10 Summary
81(4)
4 Learning Non-Regular Languages
85(30)
4.1 Substitutability
86(3)
4.1.1 Identifying Structure
86(2)
4.1.2 Learning Using Substitutability
88(1)
4.2 Empirical Approaches
89(14)
4.2.1 Expanding and Reducing Approaches
89(1)
4.2.2 Supervised and Unsupervised Approaches
89(1)
4.2.3 Word-Based and POS-Based Approaches
90(1)
4.2.4 Description of Empirical Systems
90(12)
4.2.5 Comparison of Empirical Systems
102(1)
4.3 Issues for Evaluation
103(8)
4.3.1 Looks-Good-To-Me Approach
104(1)
4.3.2 Rebuilding Known Grammars
105(2)
4.3.3 Compare against a Treebank
107(2)
4.3.4 Language Membership
109(2)
4.4 Formal Approaches
111(2)
4.5 Summary
113(2)
5 Lessons Learned and Open Problems
115(6)
5.1 Summary
115(1)
5.2 Lessons
116(1)
5.3 Problems
116(4)
5.3.1 Learning Targets
116(2)
5.3.2 Learning Criteria
118(2)
5.4 Resources
120(1)
5.5 Final Words
120(1)
Bibliography 121(16)
Author Biographies 137