Statistical methods have turned out to be quite successful in natural language processing. During the recent years, several models of stochastic grammars have been proposed, including models based on lexicalised context-free grammars [3], tree adjoining grammars [15], or dependency grammars [2, 5]. In this exploratory paper, we propose a new model of stochastic grammar, whose originality derive...

Several grammars have been proposed for representing RNA secondary structure including pseudoknots such as simple linear tree adjoining grammar (sl-tag), extended sl-tag (esl-tag) and RNA pseudoknot grammar (rpg). The main purpose of this paper is to compare the generative power of these grammars by identifying them as subclasses of multiple context-free grammars (mcfg). Specifically, it is sho...

We present a scheme for efficiently representing a lexicaiized tree-adjoining grammar (LTAG). The propcoed representational scheme allows for structure-sharing between lexical entries and the trees associated with the lexical items. A compact organization is achieved by organizing the lexicon in a hierarchical fashion and using inheritance as well as by using lexical and syntactic rules. While ...

Tree Adjoining Grammar (TAG) is u formalism for natural language grammars. Some of the basic notions of TAG's were introduced in [Jo~hi,Levy, mad Takakashi I~'Sl and by [Jo~hi, l ~ l . A detailed investigation of the linguistic relevance of TAG's has been carried out in IKroch and Joshi,1985~. In this paper, we will describe some new results for TAG's, espe¢ially in the following areas: (I) par...

Many TAG-based systems employ a particular tree adjoining grammar to generate the intended structures of the set of sentences they aim to describe. However, in most cases, the underlying set of elementary trees is more or less hand-made or maybe derived from a given tree data-base. We present a formal framework that allow to specify tree adjoining grammars by logical formulae. Based on this for...

In this paper two methods of how to make derivation in a Tree Adjoining Grammar a regular process without loss of expressive power are presented and compared. In a TAG, derivation is based upon the expansion of tree nodes into other trees. One regularization method is based on an algebraic operation called Lifting, while the other exploits an additional spatial dimension by transforming the com...

Fei Xia Department of Computer and Information Science University of Pennsylvania 3401 Walnut Street, Suite 400A Philadelphia PA 19104, USA [email protected] Abstract In this paper, we report our work on extracting lexicalized tree adjoining grammars (LTAGs) from partially bracketed corpora. The algorithm rst fully brackets the corpora, then extracts elementary trees (etrees), and nally l...

Language models for speech recognition typically use a probability model of the form Pr(an|a1, a2, . . . , an−1). Stochastic grammars, on the other hand, are typically used to assign structure to utterances. A language model of the above form is constructed from such grammars by computing the prefix probability ∑ w∈Σ Pr(a1 · · · anw), where w represents all possible terminations of the prefix a...