Sylvain Kahane

Pseudo-Projectivity, A Polynomially Parsable Non-Projective Dependency Grammar

Dependency grammar has a long tradition in syntactic theory, dating back to at least Tesni~res work from the thirties3 Recently, it has gained renewed attention as empirical methods in parsing are discovering the importance of relations between words (see, e.g., (Collins, 1997)), which is what dependency grammars model explicitly do, but context-free phrasestructure grammars do not. One problem that has posed an impediment to more wide-spread acceptance of dependency grammars is the fact that there is no computationally tractable version of dependency grammar which is not restricted to projective analyses. However, it is well known that there are some syntactic phenomena (such as wh-movement in English or clitic climbing in Romance) that require nonprojective analyses. In this paper, we present a form of projectivity which we call pseudoprojectivity, and we present a generative stringrewriting formalism that can generate pseudoprojective analyses and which is polynomially parsable. The paper is structured as follows. In Section 2, we introduce our notion of pseudoprojectivity. We briefly review a previously proposed formalization of projective dependency grammars in Section 3. In Section 4, we extend this formalism to handle pseudo-projectivity. We informally present a parser in Section 5.

Word Order in German: A Formal Dependency Grammar Using a Topological Hierarchy

This paper proposes a description of German word order including phenomena considered as complex, such as scrambling, (partial) VP fronting and verbal pied piping. Our description relates a syntactic dependency structure directly to a topological hierarchy without resorting to movement or similar mechanisms.

Polarized Unification Grammars

This paper proposes a generic mathematical formalism for the combination of various structures: strings, trees, dags, graphs and products of them. The polarization of the objects of the elementary structures controls the saturation of the final structure. This formalism is both elementary and powerful enough to strongly simulate many grammar formalisms, such as rewriting systems, dependency grammars, TAG, HPSG and LFG.

A Fully Lexicalized Grammar for French Based on Meaning-Text Theory

The paper presents a formal lexicalized dependency grammar based on Meaning-Text theory. This grammar associates semantic graphs with sentences. We propose a fragment of a grammar for French, including the description of ex- tractions. The main particularity of our grammar is it that it builds bubble trees as syntactic representations, that is, trees whose nodes can be filled by bubbles, which can contain others nodes. Our grammar needs more complex operations of combination of elementary structures than other lexicalized grammars, such as TAG or CG, but avoids the multiplication of elementary structures and provides linguistically well-motivated treatments.

What Is a Natural Language and How to Describe It? Meaning-Text Approaches in Contrast with Generative Approaches

The paper expounds the general conceptions of the Meaning- Text theory about what a natural language is and how it must be de- scribed. In a second part, a formalization of these conceptions - the transductive grammars - is proposed and compared with generative ap- proaches.

Dependency Annotation Choices : Assessing Theoretical and Practical Issues of Universal Dependencies

This article attempts to place dependency annotation options on a solid theoretical and applied footing. By verifying the validity of some basic choices of the current dependency reference framework, Universal Dependencies (UD), in a perspective of general annotation principles, we show how some choices can lead to inconsistencies and discontinuities, partly due to UD’s alternation between syntax and semantics. For some constructions, we propose better suited alternative structures with a clear-cut distinction of syntax and semantics. We propose a classification of conception-oriented, annotatororiented, and finally, treebank end-useroriented considerations to be used in the creation of new annotation schemes.

Syntactic Polygraphs. A Formalism Extending Both Constituency and Dependency

Syntactic analyses describe grouping operations that explain how words are combined to form utterances. The nature of these operations depends on the approach. In a constituency-based approach, grouping operations are ordered, or stratified, part-whole relations. In a dependency-based approach, grouping operations identify a governor (or head), i.e. they are directed hierarchical relations between words. It is possible to convert a constituency tree into a dependency tree by dereifying the nodes, by identifying the governor and by removing the stratification of the part-whole relations. Polygraphs combine the two types of information into a single structure and are therefore a more powerful formalism. By relaxing constraints, polygraphs also allow to underspecify both kinds of information.

A Polynomial Parsing Algorithm for the Topological Model: Synchronizing Constituent and Dependency Grammars, Illustrated by German Word Order Phenomena

This paper describes a minimal topology driven parsing algorithm for topological grammars that synchronizes a rewriting grammar and a dependency grammar, obtaining two linguistically motivated syntactic structures. The use of non-local slash and visitor features can be restricted to obtain a CKY type analysis in polynomial time. German long distance phenomena illustrate the algorithm, bringing to the fore the procedural needs of the analyses of syntax-topology mismatches in constraint based approaches like for example HPSG.

Word Ordering as a Graph Rewriting Process

This paper shows how the correspondence between a unordered dependency tree and a sentence that expresses it can be achieved by transforming the tree into a string where each linear precedence link corresponds to one specific syntactic relation. We propose a formal grammar with a distributed architecture that can be used for both synthesis and analysis. We argue for the introduction of a topological tree as an intermediate step between dependency syntax and word order.