"Word Sense Disambiguation - PowerPoint"
AN INTRODUCTION TO TREE ADJOINING GRAMMAR Rajat Kumar Mohanty 9/14/2012 1 OUTLINE • XTAG System • Basics of TAG Formalism • Operations • Constraints • Tree Families • Feature Structure 9/14/2012 2 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) 9/14/2012 3 XTAG System: An Overview Input Sentence Morph Analyzer POS Tagger Morph DB POS Blender Stat. DB Trees DB Tree Selection Syn DB Tree Grafting Derivation Structure Source: The XTAG Research Group, 2001 9/14/2012 4 Diverse Linguistic Resources • Subcategorization information (argument structure) • Syntax of various constructions (specific transformations) • Frequency information • Morphological information 9/14/2012 5 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. 9/14/2012 6 I: Initial Tree S like NP0 VP V NP1 like 9/14/2012 7 A: Auxiliary Tree S yesterday Ad S* yesterday 9/14/2012 8 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. 9/14/2012 9 Substitution S saw NP NP S John Mary NP0 VP N N NP0 VP V NP1 V NP1 John Mary N N saw John saw Mary 9/14/2012 10 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. 9/14/2012 11 Adjunction S bought has S NP0 VP VP NP0 VP V NP1 V VP* V VP has V NP1 bought has bought 9/14/2012 12 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. 9/14/2012 13 Derivation in Tree Adjoining Grammar • Derived Tree • Derivation Tree 9/14/2012 14 Derived Tree in TAG S Ad S NP0 VP N V NP1 N Yesterday John saw Mary 9/14/2012 15 Derivation Tree in TAG saw John (1) Mary (2.2) yesterday (0) 9/14/2012 16 Declarative Intransitive Tree Family [Tnx0V] Sr [ ] nx0V  NP0 [ ] VP [ ]  V< > The intransitive verbs (e.g., sleep, dance, etc. )select this Tree family [Tnx0V]. 9/14/2012 17 Ergative Tree Family [TEnx1V] Sr [ ] nx1V  NP1 [ ] VP [ ]  V< > The ergative verbs (e.g., sink, melt, etc. )select this Tree family [Tnx1V]. 9/14/2012 18 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. 9/14/2012 19 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. 9/14/2012 20 Transitive Tree with Object NP Extraction [Wnx1nx0Vnx1] This problem, I solved. St [ ]  NP1 [ ] Sr [ ]  NP0 [ ] VP[ ]  V< > NP1 [ ] NA 9/14/2012 21 Transitive Tree with object Wh-NP Extraction [Wnx1nx0Vnx1] What did he eat? Sq [ ]  NP1 [ ] Sr [ ]  NP0 [ ] VP[ ]  V< > NP1 [ ] NA 9/14/2012 22 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. 9/14/2012 23 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. 9/14/2012 24 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. 9/14/2012 25