tree substitution grammar derivations

Ngày tải lên: 23/03/2014, 16:20

... 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 ... Model Synchronous tree- substitution grammar is a for- malism for synchronously generating a pair of non-isomorphic source and target trees (Eisner, 2003). Every grammar rule is a pair of elemen- tary trees ... Learning an STSG from aligned trees is tantamount to determining a segmentation of the trees into elementary trees of the grammar along with an alignment of the elementary trees (see Figure 1 for an...

Ngày tải lên: 07/03/2014, 22:20

Ngày tải lên: 17/03/2014, 02:20

Ngày tải lên: 30/03/2014, 21:20

... 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 ... Tree Substitution Grammar (PTSG) assigns a probability to each rule in the grammar. The probability of a derivation is defined as the product of the probabilities of its component elementary trees ... Accurate Parsing with an All-Fragments Grammar. In In Proc. of ACL, pages 1098–1107. Phil Blunsom and Trevor Cohn. 2010. Unsupervised Induction of Tree Substitution Grammars for Depen- dency Parsing....

Ngày tải lên: 19/02/2014, 19:20

Ngày tải lên: 20/02/2014, 18:20

... easily and transparently. Tree adjoining grammars (TAGs) (Joshi, Levy and Takahashi, 1975, Vijay-Shanker and Joshi, 1988) possess trees as basic grammar structures, and grammar rules are used ... tree with that of the tree into which it is adjoined. In this way, a more complete description of the final tree is gradually constructed. However, in FTAG tree descriptions the internal tree ... specified trees in order to obtain more complex fully specified trees. In TUG, partially specified trees are combined (not modified) in order to ohtain a more fully specified complex tree. Feature...

Ngày tải lên: 21/02/2014, 20:20

... elements of the set of subtrees of the tree : such a relation is called a string- tree correspondence. An example of a string -tree correspondence is given in fig. I. TREE: NP I [ 4 NP 2 :AP ... of grammar rules applied (as in derivation trees). The inclusion of the substring-subtree correspondence is also another characteristic of the grammar formalism. One also sees that the grammar ... STRING -TREE CORRESPONDENCE GRAMMAR: A DECLARATIVE GRAMMAR FORMALISM FOR DEFINING THE CORRESPONDENCE BETWEEN STRINGS OF TERMS AND TREE STRUCTURES YUSOFF ZAHARIN Groupe...

Ngày tải lên: 22/02/2014, 10:20

... auxiliary tree is called the spine of the auxiliary tree. An elementary tree is either an initial tree or an auxiliary tree. We use a to refer to initial trees and/3 for auxiliary trees. A ... inputs. 5 Derivation versus Derived Trees in TAG For grammar formalisms involving the derivation of trees, a tree is called a derived tree with respect to a given grammar if it can be derived using ... rules of the grammar. A derivation tree of the grammar, on the other hand, is a tree that encodes the sequence of rewritings used in deriving a derived tree. In the case of cfg, a tree that is...

Ngày tải lên: 22/02/2014, 10:20

... 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 ... Bayesian Learning of a Tree Substitution Grammar. Association for Com- putational Linguistics. Matt Post. 2011. Judging Grammaticality with Tree Sub- stitution Grammar Derivations. Association ... 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...

Ngày tải lên: 07/03/2014, 18:20

... Abstract Treebanks, such as the Penn Treebank (PTB), offer a simple approach to obtaining a broad coverage grammar: one can simply read the grammar off the parse trees in the treebank. While ... (4) ii. NP (5) DT NN CC DT NN 4 Grammar Compaction The idea of partiality of structure in treebanks and their grammars suggests a route by which treebank grammars may be reduced in size, ... defined) are elimin- ated from the grammar. Our experiments on compacting a PTB tree- 1 For the complete investigation of the grammar ex- tracted from the Penn Treebank II see (Gaizauskas, 1995)...

Ngày tải lên: 08/03/2014, 05:21

... capability of synchronous tree adjoin- ing grammars. Computational Intelligence, 10(4). K. Vijay-Shanker and D.J. Weir. 1993. The use of shared forests in tree adjoining grammar parsing. In Proceedings ... each substitution of initial tree a¢ with predicate variable w into "),¢ at node address U, emit (¢, arg(v , r/), w) • For each modifier adjunction of auxil- iary tree/ 3¢ into tree ... target derivations, where each predicate node in the source dependency graph is linked to a set of possible elementary trees in the target grammar, each of which is instanti- ated with substitution...

Ngày tải lên: 08/03/2014, 06:20

... operations to produce derived trees recognized by the grammar. In substitu- tion, the root of the first tree is identified with a leaf of the second tree, called the substitution site. Adjoining ... operation, where the first tree replaces the subtree of the second tree rooted at a node called the adjunction site; that subtree is then substituted back into the first tree at a distinguished ... node. Elementary trees without foot nodes are called INITIAL trees and can only substitute; trees with foot nodes are called AUXILIARY trees, and must adjoin. (The symbol $ marks substitution...

Ngày tải lên: 08/03/2014, 21:20

... 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 ... improve parsing accuracy. 1 Introduction Tree Substitution Grammar (TSG) is a compelling grammar formalism which allows nonterminal rewrites in the form of trees, thereby enabling the modelling ... 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...

Ngày tải lên: 17/03/2014, 00:20

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Ngày tải lên: 31/03/2014, 01:20

Ngày tải lên: 31/03/2014, 18:20

... Description Grammars There is a range of grammar formalisms which depart from Tree Adjoining Grammar (TAG) by taking as basic building blocks tree descriptions rather than trees. D -Tree Grammar (DTG) ... Sentence planning as description using Tree- Adjoining Grammar. In Proceedings of ACL ’97. K. Vijay-Shanker. 1992. Using descriptions of trees in Tree Adjoining Grammars. Computational Lin- guistics, ... relevance of Tree Adjoining Grammar to generation. In Natural Language Gen- eration, chapter 16. Martinus Jijhoff Publishers, Dordrecht, Holland. L. Kallmeyer. 1999. Tree Description Grammars and Underspecified...

Ngày tải lên: 20/02/2014, 18:20