Overgeneration is the main source of computational complexity in previous principle-based parsers. This paper presents a message passing algorithm for principle-based parsing that avoids the overgeneration problem. This algorithm has been implemented in C++ and successfully tested with example sentences from (van Riemsdijk and Williams, 1986). 1. Introduction Unlike rule-based grammars that use a large number of rules to describe patterns in a language, Government-Binding (GB) Theory (Chomsky, 1981; Haegeman, 1991; van Riemsdijk and Williams, 1986) explains these patterns in terms of more foundmental and universal principles. A key issue in building a principle-based parser is how to procedurally interpret the principles. Since GB principles are constraints over syntactic structures, one way to implement the principles is to 1. generate candidate structures of the sentence that satisfy X-bar theory and subcategorization frames of the words in the sentence. 2. filter out structures tha...

The ParseTalk model of concurrent, object-oriented natural language parsing is introduced. It builds upon the complete lexical distribution of grammatical knowledge and incorporates inheritance mechanisms in order to express generalizations over sets of lexical items. The grammar model integrates declarative well-formedness criteria constraining linguistic relations between heads and modifiers, and procedural specifications of the communication protocol for establishing these relations. The parser's computation model relies upon the actor paradigm, with concurrency entering through asynchronous message passing. We consider various extensions of the basic actor model as required for distributed natural language understanding and elaborate on the semantics of the actor computation model in terms of event type networks (a graph representation for actor grammar specifications) and event networks (graphs which represent the actor parser's behavior). Besides theoretical claims, we present an interactive grammar/parser workbench, a graphical development environment with various types of browsers, tracers, inspectors and debuggers that has been adapted to the requirements of large-scale grammar engineering in a distributed, object-oriented specification and programming framework.

Abstract. A grammar model for concurrent, object-oriented natural language parsing is introduced. Complete lexical distribution of grammatical knowledge is achieved building upon the head-oriented notions of valency and dependency, while inheritance mechanisms are used to capture lexical generalizations. The underlying concurrent computation model relies upon the actor paradigm. We consider message passing protocols for establishing dependency relations and ambiguity handling. 1

Linguistic ambiguity is the greatest obstacle to achieving practical computational systems for natural language understanding. By contrast, people experience surprisingly little difficulty in interpreting ambiguous linguistic input. This dissertation explores distributed computational techniques for mimicking the human ability to resolve syntactic ambiguities efficiently and effectively. The competitive attachment theory of parsing formulates the processing of an ambiguity as a competition for activation within a hybrid connectionist network. Determining the grammaticality of an input relies on a new approach to distributed communication that integrates numeric and symbolic constraints on passing features through the parsing network. The method establishes syntactic relations both incrementally and efficiently, and underlies the ability of the model to establish long-distance syntactic relations using only local communication within a network. The competitive distribution of numeric ev...

We present a processing model that integrates some important psychological claims about the human sentence parsing mechanism, namely that processing is influenced by limitations on working memory and by various syntactic preferences. The model uses time-constraint information to resolve conflicting preferences in a psychologically plausible way. The starting point for this proposal is the Sausage Machine model (Frazier and Fodor, 1978; Fodor and Frazier, 1980). From there, we attempt to overcome the original model's dependence on ad hoc aspects of its grammar, and its omission of verb-frame preferences. We also add mechanisms for lexical disambiguation and semantic processing in parallel with syntactic processing.

The parsing component of previous principle-based parsers are inefficient since they tend to adopt a generate-and-test paradigm. We combine the benefits of a message-passing paradigm with the benefits of a parametric approach in the implementation of a parser that avoids overgeneration and is easily ported to multiple languages. The algorithm has been implemented in C++ and successfully tested on well-known, translationally divergent sentences. We are currently incorporating the parser into a machine translation (MT) system called PRINCITRAN.

The ParseTalk model of concurrent, object-oriented natural language parsing is introduced. It builds upon the complete lexical distribution of grammatical knowledge and incorporates inheritance mechanisms in order to express generalizations over sets of lexical items. The grammar model integrates declarative well-formedness criteria constraining linguistic relations between heads and modifiers, and procedural specifications of the communication protocol for establishing these relations. The parser's computation model relies upon the actor paradigm, with concurrency entering through asynchronous message passing. We consider various extensions of the basic actor model as required for distributed natural language understanding and elaborate on the semantics of the actor computation model in terms of event type networks (a graph representation for actor grammar specifications) and event networks (graphs which represent the actor parser's behavior). Besides theoretical claims, we present an interactive grammar/parser workbench, a graphical development environment with various types of browsers, tracers, inspectors and debuggers that has been adapted to the requirements of large-scale grammar engineering in a distributed, object-oriented specification and programming framework. 2 1

A problem in using principle-based parsers in building natural language software tools centres around the difficulty of recovering information represented at various levels of the grammar. The information encoded in the representations at the levels of D-Structure, S-Structure, and Logical Form (LF) increases monotonically. While D-Structure and S-Structure are relatively easy to recover, LF presents numerous problems for a single-pass parser. Some of of the constraints which apply to the human parsing mechanism are considered, and a single-pass principle-based parser which recovers an LF representation is presented. This single parsing mechanism is shown to parse both English and Chinese wh-questions. The mechanism which allows it to deal with English and Chinese also solves a parsing dilemma involving some complex English constructions. 1 Introduction In recent years, principle-based parsers have become ever more popular; see, among others, [2, 4, 6, 10, 11, 13, 21, 24, 28]. The li...

A framework for concurrent, object-oriented natural language parsing is introduced. The underlying grammar model is fully lexicalized, headdriven, dependency-oriented, and structured along multiple inheritance hierarchies. The computation model relies upon the actor paradigm, with concurrency entering through asynchronous message passing. Protocols for establishing basic dependency relations and for coping with structural ambiguities and text-level anaphora are considered.