Simpler TAG semantics through synchronization

In recent years Laura Kallmeyer, Maribel Romero, and their collaborators have led research on TAG semantics through a series of papers refining a system of TAG semantics computation. Kallmeyer and Romero bring together the lessons of these attempts with a set of desirable properties that such a system should have. First, computation of the semantics of a sentence should rely only on the relationships expressed in the TAG derivation tree. Second, the generated semantics should compactly represent all valid interpretations of the input sentence, in particular with respect to quantifier scope. Third, the formalism should not, if possible, increase the expressivity of the TAG formalism. We revive the proposal of using synchronous TAG (STAG) to simultaneously generate syntactic and semantic representations for an input sentence. Although STAG meets the three requirements above, no serious attempt had previously been made to determine whether it can model the semantic constructions that have proved difficult for other approaches. In this paper we begin exploration of this question by proposing STAG analyses of many of the hard cases that have spurred the research in this area. We reframe the TAG semantics problem in the context of the STAG formalism and in the process present a simple, intuitive base for further exploration of TAG semantics. We provide analyses that demonstrate how STAG can handle quantifier scope, long-distance WH-movement, interaction of raising verbs and adverbs, attitude verbs and quantifiers, relative clauses, and quantifiers within prepositional phrases.Engineering and Applied Science

Synchronous Vector TAG for Syntax and Semantics: Control Verbs, Relative Clauses, and Inverse Linking

Recent work has used the synchronous tree-adjoining grammar (STAG) formalism to demonstrate that many of the cases in which syntactic and semantic derivations appeared to be divergent could be handled elegantly through synchronization. This research has provided syntax and semantics for diverse and complex lin- guistic phenomena. However, certain hard cases push the STAG formalism to its limits, requiring awkward analyses or leaving no clear solution at all. In this paper a new variant of STAG, synchronous vector TAG (SV-TAG), and demonstrate that it has the potential to handle hard cases such as control verbs, relative clauses, and in- verse linking, while maintaining the simplicity of previous STAG syntax-semantics analyses.Engineering and Applied Science

Efficiently Parsable Extensions to Tree-Local Multicomponent TAG

Recent applications of Tree-Adjoining Grammar (TAG) to the domain of semantics as well as new attention to syntactic phenomena have given rise to increased interested in more expressive and complex multicomponent TAG formalisms (MCTAG). Although many constructions can be modeled using tree-local MCTAG (TL-MCTAG), certain applications require even more flexibility. In this paper we suggest a shift in focus from constraining locality and complexity through tree- and set-locality to constraining locality and complexity through restrictions on the derivational distance between trees in the same tree set in a valid derivation. We examine three formalisms, restricted NS-MCTAG, restricted Vector-TAG and delayed TL-MCTAG, that use notions of derivational distance to constrain locality and demonstrate how they permit additional expressivity beyond TL-MCTAG without increasing complexity to the level of set local MCTAG.Engineering and Applied Science

Complexity, Parsing, and Factorization of Tree-Local Multi-Component Tree-Adjoining Grammar

Tree-Local Multi-Component Tree-Adjoining Grammar (TL-MCTAG) is an appealing formalism for natural language representation because it arguably allows the encapsulation of the appropriate domain of locality within its elementary structures. Its multicomponent structure allows modeling of lexical items that may ultimately have elements far apart in a sentence, such as quantifiers and Wh-words. When used as the base formalism for a synchronous grammar, its flexibility allows it to express both the close relationships and the divergent structure necessary to capture the links between the syntax and semantics of a single language or the syntax of two different languages. Its limited expressivity provides constraints on movement and, we posit, may have generated additional popularity based on a misconception about its parsing complexity. Although TL-MCTAG was shown to be equivalent in expressivity to TAG when it was first introduced (Weir 1988), the complexity of TL-MCTAG is still not well-understood. This paper offers a thorough examination of the problem of TL-MCTAG recognition, showing that even highly restricted forms of TL-MCTAG are NP-complete to recognize. However, in spite of the provable difficulty of the recognition problem, we offer several algorithms that can substantially improve processing efficiency. First, we present a parsing algorithm that improves on the baseline parsing method and runs in polynomial time when both the fan-out and rank of the input grammar are bounded. Second, we offer an optimal, efficient algorithm for factorizing a grammar to produce a strongly-equivalent TL-MCTAG grammar with the rank of the grammar minimized.Engineering and Applied Science

Rational Coordinated Anaphora Theory

Rational Coordinated Anaphora theory is a novel explanatory theory that predicts how speakers generate anaphoric referring expressions in discourse, how hearers interpret them, and how all conversational participants coordinate their strategies to promote clear communication while minimizing effort. Its main premise is that conversational participants are, and expect each other to be rational. This paper presents Rational Coordinated Anaphora theory in detail and then contrasts it with Centering theory, demonstrating the reason for the robustness of Centering theory's main premise, Rule 1, and explaining some of Centering theory's previously puzzling limitations.Engineering and Applied Science

Extraction phenomena in synchronous TAG syntax and semantics

We present a proposal for the structure of noun phrases in Synchronous Tree-Adjoining Grammar (STAG) syntax and semantics that permits an elegant and uniform analysis of a variety of phenomena, including quantifier scope and extraction phenomena such as wh-questions with both moved and in-place wh-words, pied-piping, stranding of prepositions, and topicalization. The tight coupling between syntax and semantics enforced by the STAG helps to illuminate the critical relationships and filter out analyses that may be appealing for either syntax or semantics alone but do not allow for a meaningful relationship between them.