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Rajat Kumar Mohanty

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.)

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Rajat Kumar Mohanty

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  1. Rajat Kumar Mohanty AN INTRODUCTION TO TREE ADJOINING GRAMMAR

  2. OUTLINE • XTAG System • Basics of TAG Formalism • Operations • Constraints • Tree Families • Feature Structure

  3. 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)

  4. XTAG System: An Overview Input Sentence Morph Analyzer POS Tagger Morph DB Stat. DB POS Blender Syn DB Trees DB Tree Selection Tree Grafting Derivation Structure Source: The XTAG Research Group, 2001

  5. Diverse Linguistic Resources • Subcategorization information (argument structure) • Syntax of various constructions (specific transformations) • Frequency information • Morphological information

  6. A Tree Adjoining Grammar (TAG) consists of a quintuple (, NT, I, A, S) •  is a finite set of terminal symbols; • NT is a finite set of non-terminal symbols:  NT = ; • S is a distinguished non-terminal symbol: S  NT; • I is a set of finite trees, called initial trees; • A is a finite set of finite trees, called auxiliary trees.

  7. I: Initial Tree S like NP0 VP V NP1  like

  8. A: Auxiliary Tree S yesterday Ad S* yesterday

  9. Operations in Tree Adjoining Grammar • Substitution The 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.

  10. Substitution NP John N John NP Mary N Mary S  NP0 VP V NP1 N N John saw Mary S saw NP0 VP V NP1  saw

  11. 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.

  12. Adjunction S  NP0 VP V VP has V NP1 bought S bought NP0 VP V NP1  bought has VP V VP* has

  13. 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.

  14. Derivation in Tree Adjoining Grammar • Derived Tree • Derivation Tree

  15. Derived Tree in TAG S  Ad S NP0 VP N V NP1 N Yesterday John saw Mary

  16. Derivation Tree in TAG saw John (1) Mary (2.2) yesterday (0)

  17. Declarative Intransitive Tree Family [Tnx0V] Sr [ ] nx0V [ ] NP0 [ ] VP [ ] [ ] V< > The intransitive verbs (e.g., sleep, dance, etc. )select this Tree family [Tnx0V].

  18. Ergative Tree Family [TEnx1V] Sr [ ] nx1V [ ] NP1 [ ] VP [ ] [ ] V< > The ergative verbs (e.g., sink, melt, etc. )select this Tree family [Tnx1V].

  19. Declarative Transitive Tree Family [Tnx0Vnx1] Sr[ ] nx0Vnx1 [ ] NP0[] VP [ ] [ ] V< > NP1 [ ] The transitive verbs (e.g., eat, like, hit, etc. )select this Tree family [Tnx0Vnx1]. e.g., I ate an apple.

  20. Declarative Ditransitive Tree Family [Tnx0Vnx1pnx2] Sr [ ] nx0Vnx1pnx1 [ ] 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.

  21. Transitive Tree with Object NP Extraction [Wnx1nx0Vnx1] This problem, I solved. St[ ] [ ] NP1 [ ] Sr [ ] [ ] NP0[ ] VP[ ] [ ] V< > NP1 [ ] NA 

  22. Transitive Tree with object Wh-NP Extraction [Wnx1nx0Vnx1] What did he eat? Sq[ ] [ ] NP1 [ ] Sr [ ] [ ] NP0[ ] VP[ ] [ ] V< > NP1 [ ] NA 

  23. 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.

  24. 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.

  25. 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.

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