UDRT-based Semantics Construction for LTAG

Lexicalized Tree Adjoining Grammars (LTAGs) [6] are tree rewriting systems consisting of a finite set of trees associated with lexical items, so-called elementary trees (etrees). Elementary trees represent extended projections of lexical items that encapsulate all their syntactic/semantic arguments. Due to this property, semantics construction in LTAG can be based on elementary trees as basic units, and is typically performed on the basis of the derivation tree, which records the history of how elementary trees are combined by substitution and adjunction operations. However, it has been argued by Frank and van Genabith [3] that the derivation tree is not an appropriate structure for principle-based semantics construction in that the derivation tree neither mirrors the phrase structure nor the dependency structure of the sentence. It is essentially due to the adjunction operation that dependencies that are crucial for a principle-based semantics construction procedure are not available from the derivation tree. Instead, Frank and van Genabith propose to define semantics construction on the basis of the derived tree. In this paper we will have a closer look at the role that adjunction plays for semantics composition in LTAG and examine whether the semantics construction approach based on derivation trees can be rescued. The contributions of the paper are manifold. First, we show that the semantics construction approach for LDGs presented by Cimiano and Reyle [2] can in principle be applied to semantics construction for LTAG. We borrow from Cimiano and Reyle the idea of talking explicitly about labels and scope, which will turn out as a crucial component for principle-based semantics construction on the basis of the derivation tree. Second, we show that an adequate account of quantifier scope within LTAG is possible without necessarily leading to an extension of LTAG as