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Tree-Adjoining Grammars Definition (Tree-Adjoining Grammar) A tree-adjoining grammar (TAG) is a 5-tuple G = (N, T , I , A, S) where: N is a finite set of non-terminal symbols. T is a finite set of terminal symbols, N ∩ T = ∅. I is a finite set of initial trees. A is a finite set of auxiliary trees. S ∈ N is a specific start symbol. The trees in I ∪ A are called elementary trees. A Tree-Substitution Grammar (TSG) is defined analogously as a 4-tuple G = (N, T , I , S), i.e. a TAG without auxiliary trees. 16 / 52
Initial Trees Definition (Initial Tree) An initial tree is characterized as follows: Example Internal nodes are only labeled by non-terminal symbols. Leaf nodes are labeled by terminals or non-terminals. If a leaf is labeled by a non-terminal, it is marked as substitution node (indicated by the symbol “↓”). D NP NP S S a D↓ N N NP↓ VP NP↓ VP cat Mary V NP↓ V NP↓ PP saw gives P NP↓ to 17 / 52
Page 1 and 2: Lexicalized Tree-Adjoining Grammars
Page 3 and 4: Context-Free Grammars Definition (C
Page 5 and 6: Tree-Substitution Grammars Example
Page 7 and 8: Outline 1 Why CFGs are not enough (
Page 9 and 10: Cross-Serial Dependencies Example (
Page 11 and 12: Lexicalization Example (Lexicalized
Page 13 and 14: Lexicalization Example (CFG which i
Page 15: Outline 1 Why CFGs are not enough (
Page 19 and 20: Substitution Definition (Substituti
Page 21 and 22: Adjunction Definition (Adjunction)
Page 23 and 24: Adjunction Constraints Given TAG G
Page 25 and 26: Lexicalization Example (strong lexi
Page 27 and 28: Further Formal Properties of TAL Tr
Page 29 and 30: TAG Parsing Parser: Given a string
Page 31 and 32: Recognizing Adjunction But the algo
Page 33 and 34: Dotted Tree We introduce the notion
Page 35 and 36: Chart Items The algorithm stores in
Page 37 and 38: Scan Operations Input string: c 1
Page 39 and 40: Complete Operations 1 2 3 [γ, adr,
Page 41 and 42: Recognizer Algorithm Algorithm (Rec
Page 43 and 44: Complexity of Recognizer Given: n:
Page 45 and 46: Recognizing Substitution Recognizer
Page 47 and 48: LTAG-Spinal Parser LTAG-spinal: Rou
Page 49 and 50: LTAG-Spinal Parser Graphical repres
Page 51 and 52: Conclusion TAG: a grammar formalism

Lexicalized Tree-Adjoining Grammars (LTAG) - ad-teaching.infor...

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