bayesian tree substitution grammars

... July 2010. c 2010 Association for Computational Linguistics Blocked Inference in Bayesian Tree Substitution Grammars Trevor Cohn Department of Computer Science University of Sheffield T.Cohn@dcs.shef.ac.uk Phil ... Oxford Phil.Blunsom@comlab.ox.ac.uk Abstract Learning a tree substitution grammar is very challenging due to derivational am- biguity. Our recent approach used a Bayesian non-parametric model to induce good derivations from treebanked input (Cohn ... supervised scenario where treebanked data is available. This is because treebanks are typically not annotated with their TSG derivations (how to decompose a tree into elementary tree fragments); instead...

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Ngày tải lên: 23/03/2014, 16:20

... symbol refinement without heuristics. 3 Symbol-Refined Tree Substitution Grammars In this section, we propose Symbol-Refined Tree Substitution Grammars (SR-TSGs) for syntactic parsing. Our SR-TSG ... of parse trees in an unsupervised fashion. That is, we wish to infer the symbol sub- categories of every node and substitution site (i.e., nodes where substitution occurs) from parse trees. Extracted ... 25:855–900. Matt Post and Daniel Gildea. 2009. Bayesian Learning of a Tree Substitution Grammar. In In Proc. of ACL- IJCNLP, pages 45–48. Yee Whye Teh. 2006a. A Bayesian Interpretation of Interpolated...

Ngày tải lên: 19/02/2014, 19:20

... Inducing Compact but Accurate Tree- Substitution Grammars. In Proceedings NAACL. Trevor Cohn, and Phil Blunsom 2010. Blocked inference in Bayesian tree substitution grammars. Association for Computational ... with Tree Substitution Grammars Ben Swanson Brown University chonger@cs.brown.edu Eugene Charniak Brown University ec@cs.brown.edu Abstract We investigate the potential of Tree Substitu- tion Grammars ... and Daniel Gildea. 2009. Bayesian Learning of a Tree Substitution Grammar. Association for Com- putational Linguistics. Matt Post. 2011. Judging Grammaticality with Tree Sub- stitution Grammar...

Ngày tải lên: 07/03/2014, 18:20

... syn- chronous tree- substitution (Eisner, 2003) or tree- adjoining grammars may better capture the pair- ings. In this work, we explore techniques for inducing synchronous tree- substitution grammars ... parallel parse trees and availability of word align- ments, yet the unavailability of large-scale data, calling for a Bayesian tree- to -tree formalism. We formalize nonparametric Bayesian STSG ... shieber}@seas.harvard.edu Abstract We describe our experiments with training algorithms for tree- to -tree synchronous tree- substitution grammar (STSG) for monolingual translation tasks such as sentence compression...

Ngày tải lên: 07/03/2014, 22:20

... AFNLP Bayesian Learning of a Tree Substitution Grammar Matt Post and Daniel Gildea Department of Computer Science University of Rochester Rochester, NY 14627 Abstract Tree substitution grammars ... apply these techniques to learn a tree substitution gram- mar, evaluate it on the Wall Street Journal parsing task, and compare it to previous work. 2 Model 2.1 Tree substitution grammars TSGs extend CFGs ... subtrees sizes used in pars- ing WSJ§23 (filled points), as well as from the grammars themselves (outlined points). over subtree size. They substantially outperform heuristically extracted grammars...

Ngày tải lên: 17/03/2014, 02:20

... pair, (b) a tree transformation based mapping, and (c) a tree trans- ducer that performs the mapping. volve tree transformations either between two trees or a tree and a string. The tree transducer, ... and grammars on trees. Mathe- matical Systems Theory 4, pages 257–287, 1970. Stuart M. Shieber. Synchronous grammars as tree trans- ducers. In Proc. of the Seventh International Workshop on Tree ... scores are in bold, while the highest among the tree based models are marked with a bullet. The dotted line separates the tree based from non -tree based models. 7 and describing a general purpose...

Ngày tải lên: 19/02/2014, 19:20

... trees and .A is a set of auxiliary trees. Trees in :TU.A are also called elementary trees. We refer to the root of an elementary tree t as Rt. Each auxiliary tree has exactly one distin- guished ... context-free grammars. Computational Linguis- tics, 17(3):315-323. A. K. Joshi and Y. Schabes. 1992. Tree- adjoining gram- mars and lexicalized grammars. In M. Nivat and A. Podelski, editors, Tree ... foot. We refer to the foot of an auxiliary tree t as Ft. We let V denote the set of all nodes in the elementary trees. For each leaf N in an elementary tree, except when it is a foot, we define...

Ngày tải lên: 20/02/2014, 18:20

... (predicate-argument) constraints. Elementary trees are of two kinds - (a) INITIAL TREES and (b) AUX- ILIARY TREES. Nodes on the frontier of initial trees are marked as substitution sites by a '~'. ... training corpus. Auxiliary trees in LTAG represent recursive struc- tures. So if there is an auxiliary tree that is used in an LTAG parse, then that tree with the trees for its arguments can ... (l~niladdp~Ja] (2.2) ~ Pbl~ael: (b) (c) Figure 2: (as and/~s) Elementary trees, (a) Derived Tree, (b) Derivation Tree, and (c) Dependency tree for the sentence: show me the flights from Boston to Philadelphia....

Ngày tải lên: 20/02/2014, 22:20

... produces a tree description. We still need to solve this de- scription in order to obtain trees (i.e. the items of the resulting grammar). Constraint-based tree description solver The tree description ... constraints on the tree de- scriptions besides tree- shaping them. These pa- rameters are called principles in the XMG termi- nology. Some are specific to a target formalism (e.g. TAG trees must have ... and Duchier, 2004). At the end of this tree description solving pro- cess we obtain the trees of the grammar. Note that the use of constraint programming techniques to solve tree descriptions allows us...

Ngày tải lên: 22/02/2014, 02:20

... abbreviatory device for listing a finite set of elementary trees), since it is impossible to adjoin one tree into another tree of the same tree set. There are several other syntactic issues which ... Aravind: K., August 1988. Parsing Strategies with 'Lexiealized' Grammars: Application to Tree Ad- joining Grammars. In Proceedings of the 12 th Interna- tional Conference on Computational ... elementary trees of TAG, allows us to "lexicalize" a TAG gram- mar: we can associate each tree in a grammar with a lexical item [Schabes et al 1988, Schabes 1990] 4. The tree will...

Ngày tải lên: 22/02/2014, 10:20

... symbol, 1 and A are two finite sets of trees, called initial trees and auxiliary trees respectively. The trees in the set IuA are called elementary trees. We assume that the reader is familiar ... Lexicalized Tree Adjoining Grammars (Schabes et al., 1988) are a refinement of TAGs such that each elementary tree is associated with a lexieal item, called the anchor of the tree. Therefore, ... to the Production of O(n 6) Earley Parsers for Tree Adjoining Grammars. In Proceedings of the 1st International Workshop on Tree Adjoining Grammars. Dagstuhl Castle, F.R.G Satta, Giorgio,...

Ngày tải lên: 22/02/2014, 10:20

... only increases by 1. Thus, simple context-free tree grammars strongly lexicalize tree adjoining grammars and themselves. 1 Introduction Tree adjoining grammars [TAG] (Joshi et al., 1969; Joshi et ... 1992. Tree- adjoining grammars and lexicalized grammars. In Maurice Nivat and Andreas Podelski, editors, Tree Au- tomata and Languages. North-Holland. Aravind K. Joshi and Yves Schabes. 1997. Tree- adjoining ... order. Second-order substitution is illustrated in Figure 2. G ´ ecseg and Steinby (1997) present a detailed intro- duction to trees and tree languages. 3 Context-free tree grammars In this section,...

Ngày tải lên: 07/03/2014, 18:20

... synchronous tree- adjoining grammars (STAGs) in terms of tree transducers (or equivalently, synchronous tree substitution grammars) is developed. Essentially, a STAG corresponds to an extended tree transducer ... assumptions on all tree- adjoining grammars (and synchronous tree- adjoining grammars) . A tree- adjoining grammar (TAG) is a finite set of initial trees and a finite set of auxiliary trees. Our 1070 Jonathan ... consist of a regular tree language and two embedded tree transducers (instead of two tree homomorphisms). Such embedded tree transduc- ers (Shieber, 2006) are particular macro tree trans- ducers...

Ngày tải lên: 17/03/2014, 00:20

... most 1 foot-node, such a tree is an auxiliary tree. Trees that are not auxiliary are initial. Elementary trees combine with 2 operations : substitution and adjunetion. Substitution is compulsory ... derivation trees : 1. Prefer the derivation tree with the fewer number of nodes 2. Prefer to attach an m -tree low 6 3. Prefer the derivation tree with the fewer number of 13 -tree nodes Principle ... same derived tree can be obtained using different derivations. This is why parsing LTAGs yields a derivation tree, from 2 Traditionally initial trees are called o~, and auxiliary trees 13 585...

Ngày tải lên: 17/03/2014, 07:20

... structure: TREENODE : <> == under <type> == internal. STREE: <> == TREENODE <cat> == s. VPTREE: <> == TREENODE <cat> ==vp <parent> == STREE:<> ... NPCOMP:<>. NPCOMP: <> == TREENODE <cat> np <type> == substitution. PPTREE: <> == TREENODE <cat> == pp. PTREE: <> == TREENODE <cat> I= p <type> ... which allows a tree- fragment to be spliced into the body of a tree. However, we only need to concern ourselves here with the representation of the trees involved, not with the substitution/ adjunction...

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