Laura Kallmeyer

Factoring Predicate Argument and Scope Semantics: Underspecified Semantics with LTAG

In this paper we propose a compositional semantics for lexicalizedtree-adjoining grammar (LTAG). Tree-local multicomponent derivationsallow separation of the semantic contribution of a lexical item into onecomponent contributing to the predicate argument structure and a secondcomponent contributing to scope semantics. Based on this idea asyntax-semantics interface is presented where the compositionalsemantics depends only on the derivation structure. It is shown that thederivation structure (and indirectly the locality of derivations) allowsan appropriate amount of underspecification. This is illustrated byinvestigating underspecified representations for quantifier scopeambiguities and related phenomena such as adjunct scope and islandconstraints.

Parsing Beyond Context-Free Grammars

Given that context-free grammars (CFG) cannot adequately describe natural languages, grammar formalisms beyond CFG that are still computationally tractable are of central interest for computational linguists. This book provides an extensive overview of the formal language landscape between CFG and PTIME, moving from Tree Adjoining Grammars to Multiple Context-Free Grammars and then to Range Concatenation Grammars while explaining available parsing techniques for these formalisms. Although familiarity with the basic notions of parsing and formal languages is helpful when reading this book, it is not a strict requirement. The presentation is supported with many illustrations and examples relating to the different formalisms and algorithms, and chapter summaries, problems and solutions. The book will be useful for students and researchers in computational linguistics and in formal language theory.

Semantic construction in feature-based TAG

We propose a semantic construction method for Feature-Based Tree Adjoining Grammar which is based on the derived tree, compare it with related proposals and briefly discuss some implementation possibilities,

Flexible Composition In Ltag: Quantifier Scope and Inverse Linking

1 Here and throughout this chapter, we will avoid using (singular) indefinites as wide scope quantifiers. This is because the wide scope effect of indefinites can be obtained through a special pseudo-scoping mechanism – namely, choice functions (Kratzer, 1998, Reinhart, 1997) –, and not through the general truly scoping mechanisms that we are concerned with in this chapter. This pseudo-scoping mechanism allows indefinites to yield the truthconditional effect of wide scope in configurations where regular quantifiers cannot, e.g., out of if-islands, as the contrast (81)-(82) illustrates. In sum, even though (83a) in the text has an ∃∀ reading, we need example (84a) to ensure that true inverse scope is available in the grammar.

Data-Driven Parsing with Probabilistic Linear Context-Free Rewriting Systems

This paper presents the first efficient implementation of a weighted deductive CYK parser for Probabilistic Linear Context-Free Rewriting Systems (PLCFRSs). LCFRS, an extension of CFG, can describe discontinuities in a straightforward way and is therefore a natural candidate to be used for data-driven parsing. To speed up parsing, we use different context-summary estimates of parse items, some of them allowing for A* parsing. We evaluate our parser with grammars extracted from the German NeGra treebank. Our experiments show that data-driven LCFRS parsing is feasible and yields output of competitive quality.

Tree-Local Multicomponent Tree-Adjoining Grammars with Shared Nodes

This article addresses the problem that the expressive power of tree-adjoining grammars (TAGs) is too limited to deal with certain syntactic phenomena, in particular, with scrambling in free-word-order languages. The TAG variants proposed so far in order to account for scrambling are not entirely satisfying. Therefore, the article introduces an alternative extension of TAG that is based on the notion of node sharing, so-called (restricted) tree-local multicomponent TAG with shared nodes (RSN-MCTAG). The analysis of some German scrambling data is sketched in order to show that this TAG extension can deal with scrambling. Then it is shown that for RSN-MCTAGs of a specific type, equivalent simple range concatenation grammars can be constructed. As a consequence, these RSN-MCTAGs are mildly context-sensitive and in particular polynomially parsable. These specific RSN-MCTAGs probably can deal not with all scrambling phenomena, but with an arbitrarily large subset.

Syntax-driven semantic frame composition in Lexicalized Tree Adjoining Grammars

The grammar framework presented in this paper combines Lexicalized Tree Adjoining Grammar (LTAG) with a (de)compositional frame semantics. We introduce elementary constructions as pairs of elementary LTAG trees and decompositional frames. The linking between syntax and semantics can largely be captured by such constructions since in LTAG, elementary trees represent full argument projections. Substitution and adjunction in the syntax then trigger the unification of the associated semantic frames, which are formally defined as base-labelled feature structures. Moreover, the system of elementary constructions is specified in a metagrammar by means of tree and frame descriptions. This metagrammatical factorization gives rise to a fine-grained decomposition of the semantic contributions of syntactic building blocks, and it allows us to separate lexical from constructional contributions and to carve out generalizations across constructions. In the second half of the paper, we apply the framework to the analysis of directed motion expressions and of the dative alternation in English, two well-known examples of the interaction between lexical and constructional meaning.

On the Relation between Multicomponent Tree Adjoining Grammars with Tree Tuples (TT-MCTAG) and Range Concatenation Grammars (RCG)

This paper investigates the relation between TT-MCTAG, a formalism used in computational linguistics, and RCG. RCGs are known to describe exactly the class PTIME; simple RCG even have been shown to be equivalent to linear context-free rewriting systems, i.e., to be mildly context-sensitive. TT-MCTAG has been proposed to model free word order languages. In general, it is NP-complete. In this paper, we will put an additional limitation on the derivations licensed in TT-MCTAG. We show that TT-MCTAG with this additional limitation can be transformed into equivalent simple RCGs. This result is interesting for theoretical reasons (since it shows that TT-MCTAG in this limited form is mildly context-sensitive) and, furthermore, even for practical reasons: We use the proposed transformation from TT-MCTAG to RCG in an actual parser that we have implemented.

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.

Local Tree Description Grammars

This paper addresses the problem of integrating underspecification of the parent (immediate dominance) and the dominance relation into tree-generating grammar formalisms for natural language processing. Retaining the advantages of Tree Adjoining Grammars (TAG), in particular extended domains of locality and a local derivation process, a TAG extension called local Tree Description Grammar (local TDG) is defined that generates tree descriptions. In contrast to earlier tree description based variants of TAG, the possibility of an underspecified dominance relation provides underspecified representations for scope ambiguities. Furthermore, local TDGs allow an adequate treatment of long-distance scrambling in German which is one of the problematic phenomena for TAG.