Timm Lichte

Characterizing discontinuity in constituent treebanks

Measures for the degree of non-projectivity of dependency grammar have received attention both on the formal and on the empirical side. The empirical characterization of discontinuity in constituent treebanks annotated with crossing branches has nevertheless been neglected so far. In this paper, we present two measures for the characterization of both the discontinuity of constituent structures and the nonprojectivity of dependency structures. An empirical evaluation on German data as well as an investigation of the relation between the measures and grammars extracted from treebanks shows their relevance.

TuLiPA: Towards a Multi-Formalism Parsing Environment for Grammar Engineering

In this paper, we present an open-source parsing environment (Tubingen Linguistic Parsing Architecture, TuLiPA) which uses Range Concatenation Grammar (RCG) as a pivot formalism, thus opening the way to the parsing of several mildly context-sensitive formalisms. This environment currently supports tree-based grammars (namely Tree-Adjoining Grammars (TAG) and Multi-Component Tree-Adjoining Grammars with Tree Tuples (TT-MCTAG)) and allows computation not only of syntactic structures, but also of the corresponding semantic representations. It is used for the development of a tree-based grammar for German.

Discontinuous parsing with continuous trees

We introduce a new method for incremental shift-reduce parsing of discontinuous constituency trees, based on the fact that discontinuous trees can be transformed into continuous trees by changing the order of the terminal nodes. It allows for a clean formulation of different oracles, leads to faster parsers and provides better results. Our best system achieves an F1 of 80.02 on TIGER.

Licensing German negative polarity items in LTAG

Our paper aims at capturing the distribution of negative polarity items (NPIs) within lexicalized Tree Adjoining Grammar (LTAG). The condition under which an NPI can occur in a sentence is for it to be in the scope of a negation with no quantifiers scopally intervening. We model this restriction within a recent framework for LTAG semantics based on semantic unification. The proposed analysis provides features that signal the presence of a negation in the semantics and that specify its scope. We extend our analysis to modelling the interaction of NPI licensing and neg raising constructions.