rajat kumar mohanty
DESCRIPTION
Rajat Kumar Mohanty. AN INTRODUCTION TO TREE ADJOINING GRAMMAR. OUTLINE. XTAG System Basics of TAG Formalism Operations Constraints Tree Families Feature Structure. 2. XTAG SYSTEM. What does it do? It takes a sentence as input, and provides: Constituency (NP, VP, PP, etc.) - PowerPoint PPT PresentationTRANSCRIPT
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Rajat Kumar Mohanty
AN INTRODUCTION TO
TREE ADJOINING GRAMMAR
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OUTLINE
• XTAG System• Basics of TAG Formalism• Operations• Constraints• Tree Families• Feature Structure
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2. XTAG SYSTEM
What does it do?It takes a sentence as input, and provides:• Constituency (NP, VP, PP, etc.) • Derivational History (how phrases are combined)• Predicate/ Argument Structure (main verb,
subject, object, etc)
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XTAG System: An Overview
Input Sentence
Morph Analyzer POS Tagger
POS Blender
Derivation Structure
Morph DB
Trees DB Syn DBTree Selection
Tree Grafting
Source: The XTAG Research Group, 2001
Stat. DB
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Diverse Linguistic Resources
• Subcategorization information (argument structure)
• Syntax of various constructions (specific transformations)
• Frequency information• Morphological information
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A Tree Adjoining Grammar (TAG) consists of a quintuple (, NT, I, A, S)
a. is a finite set of terminal symbols;b. NT is a finite set of non-terminal symbols:
NT = ;c. S is a distinguished non-terminal symbol: S
NT;d. I is a set of finite trees, called initial trees;e. A is a finite set of finite trees, called auxiliary
trees.
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I: Initial Tree
S alike
NP0 VP
V NP1
like
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A: Auxiliary Tree
S yesterday
Ad S*
yesterday
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Operations in Tree Adjoining Grammar
• SubstitutionThe substitution operation appends one tree at a frontier node of another tree. That is substitution takes place at non-terminal nodes on the frontier side, which are marked for substitution by a down arrow.
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Substitution
S asaw
NP0 VP
V NP1
saw
NP
aJohn
N
John
NP
aMary
N
Mary
S
NP0 VP
V NP1
N N
John saw Mary
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Adjunction
• The adjunction operation is more powerful.• It can be used to insert one tree within
another.• A new tree is built from an auxiliary tree
and a tree ( : initial, auxiliary or derived) by adjunction.
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Adjunction
S abought
NP0 VP
V NP1
bought
S
NP0 VP
V VP
has
V NP1
bought
has
VP
V VP*
has
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Adjoining Constraints
• Selective Adjunction: The adjunction of an auxiliary tree is not mandatory on the given node.
• Null Adjunction: It disallows any adjunction on the given node.
• Obligatory Adjunction: In this case, the adjunction of an auxiliary tree is mandatory.
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Derivation in Tree Adjoining Grammar
• Derived Tree
• Derivation Tree
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Derived Tree in TAG
S
Ad S
NP0 VP
N V NP1
N
Yesterday John saw Mary
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Derivation Tree in TAG
asaw
aJohn (1) aMary (2.2) yesterday (0)
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Declarative Intransitive Tree Family [Tnx0V]
Sr [ ] anx0V [ ]
NP0 [ ] VP [ ] [ ]
V< >
The intransitive verbs (e.g., sleep, dance, etc. )select this Tree family [Tnx0V].
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Ergative Tree Family [TEnx1V]
Sr [ ] anx1V [ ]
NP1 [ ] VP [ ] [ ]
V< > The ergative verbs (e.g., sink, melt, etc. )select this Tree family [Tnx1V].
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Sr [ ] anx0Vnx1
[ ]
NP0[] VP [ ]
[ ]
V< > NP1 [ ]
Declarative Transitive Tree Family [Tnx0Vnx1]
The transitive verbs (e.g., eat, like, hit, etc. )select this Tree family [Tnx0Vnx1]. e.g., I ate an apple.
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Declarative Ditransitive Tree Family [Tnx0Vnx1pnx2]
Sr [ ] anx0Vnx1pnx1 [ ]
NP0 [ ] VP [ ]
[ ]
V< > NP1 [ ] PP2 [ ]
The di-transitive verbs (e.g., put, usher, etc. )select this Tree family [Tnx0Vpnx1].
e.g.,The secretary ushered me into his office.
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This problem, I solved. St [ ] [ ]
NP1 [ ] Sr [ ] [ ]
NP0 [ ] VP[ ] [ ]
V< > NP1 [ ] NA
Transitive Tree with Object NP Extraction [aWnx1nx0Vnx1]
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What did he eat? Sq [ ] [ ]
NP1 [ ] Sr [ ] [ ]
NP0 [ ] VP[ ] [ ]
V< > NP1 [ ] NA
Transitive Tree with object Wh-NP Extraction [aWnx1nx0Vnx1]
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Sentential Complement Tree: [Tnx0Vnx1s2]
S r [ ] nx0Vnx1s2 [ ]
NP0[ ] VP [ ] [ ]
V<> NP1[ ] S2*[ ]
John told Mary that it was his turn.
John begged Mary to increase his disk quota.
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Complementizer Tree: [sCOMP] Sc [ ]
comp: <1> mode: <2> ind / inf COMP [comp: <1> ] Sr* [assign-comp: <1>] [comp: <>]
mode: <2> comp: nil assign-comp: <>
John told Mary that it was his turn.
John begged Mary to increase his disk quota.
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Suggested Readings
• Joshi, A. K. 1987. An Introduction to Tree Adjoining Grammars. In A. Manaster-Ramer, ed., Mathematics of Language. Amsterdam: John Benjamins.
• XTAG Research Group. 1999. A Lexicalized Tree Adjoining Grammar for English. Technical Report IRCS, University of Pennsylvania, Philadelphia.