We present a system for generating parsers based directly on the metaphor of parsing as deduction. Parsing algorithms can be represented directly as deduction systems, and a single deduction engine can interpret such deduction systems so as to implement the corresponding parser. The method generalizes easily to parsers for augmented phrase structure formalisms, such as definiteclause grammars and other logic grammar formalisms, and has been used for rapid prototyping of parsing algorithms for a variety of formalisms including variants of tree-adjoining grammars, categorial grammars, and lexicalized context-free grammars.

The unification problem and several variants are presented. Various algorithms and data structures are discussed. Research on unification arising in several areas of computer science is surveyed, these areas include theorem proving, logic programming, and natural language processing. Sections of the paper include examples that highlight particular uses

This paper gives an overall account of a prototype natural language question answering system, called Chat-80. Chat-80 has been designed to be both efficient and easily adaptable to a variety of applications. The system is implemented entirely in Prolog, a programming language based on logic. With the aid of a logic-based grammar formalism called extraposition grammars, Chat-80 translates English questions into the Prolog subset of logic. The resulting logical expression is then transformed by a planning algorithm into efficient Prolog, cf. "query optimisation" in a relational database. Finally, the Prolog form is executed to yield the answer. On a domain of world geography, most questions within the English subset are answered in well under one second, including relatively complex queries

This paper presents a grammar formalism for natural language analysis, called extraposition grammars (XGs), based on the subset of predicate calculus known as definite, or Horn, clauses. It is argued that certain important linguistic phenomena, collectively known in transformational grammar as left extra- position, can be described better in XGs than in earlier grammar formalisms based on definite clauses

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Definite Clause Grammars (DCGs) have proved valuable to computational linguists since they can be used to specify phrase structured grammars. It is well known how to encode DCGs in Horn clauses. Some linguistic phenomena, such as filler-gap dependencies, are difficult to account for in a completely satisfactory way using simple phrase structured grammar. In the literature of logic grammars there have been several attempts to tackle this problem by making use of special arguments added to the DCG predicates corresponding to the grammatical symbols. In this paper we take a different line, in that we account for filler-gap dependencies by encoding DCGs within hereditary Harrop formulas, an extension of Horn clauses (proposed elsewhere as a foundation for logic programming) where implicational goals and universally quantified goals are permitted. Under this approach, filler-gap dependencies can be accounted for in terms of the operational semantics underlying hereditary Harrop formulas, in a way reminiscent of the treatment of such phenomena in Generalized Phrase Structure Grammar (GPSG). The main features involved in this new formulation of DCGs are mechanisms for providing scope to constants and program clauses along with a mild use of λ-terms and λ-conversion. 1

This paper describes a logic grammar formalism, modifier structure grammars (MSGs), together with an interpreter written in Prolog, which can handle coordination (and other natural language constructions) in a reasonable and general way. The system produces both syntactic analyses and logical forms, and problems of scoping for coordination and quantifiers are dealt with. The MSG formalism seems of interest in its own right (perhaps even outside natural language processing) because the notions of syntactic structure and semantic interpretation are more constrained than in many previous systems (made more implicit in the formalism itself), so that less burden is put on the grammar writer

Optical Music Recognition is a particular form of document analysis in which there is much knowledge about document structure. Indeed there exists an important set of rules for musical notation, but current systems do not fully use them. We propose a new solution using a grammar to guide the segmentation of the graphical objects and their recognition. The grammar is essentially a description of the relations (relative position and size, adjacency, etc) between the graphical objects. Inspired by Definite Clause Grammar techniques, the grammar can be directly implemented in Prolog, a higher-order dialect of Prolog. Moreover, the translation from the grammar into Prolog code can be done automatically. Our approach is justified by the first encouraging results obtained with a prototype for music score recognition. Keywords: Document analysis, Optical Music Recognition, DCG, Grammar Translation 1 Introduction In structured document analysis, one open problem is to separate knowledge from...

One problem for the generation of natural language text is determining when to use a sequence of simple sentences and when a single complex one is more appropriate. In this paper, we show how focus of attention is one factor that influences this decision and describe its implementation in a system that generates explanations for a student advisor expert system. The implementation uses tests on functional information such as focus of attention within the Prolog definite clause grammar formalism to determine when to use complex sentences, resulting in an efficient generator that has the same benefits as a functional grammar system.

A unification-based grammar is a type of language description well suited for the implementation on a computer. As many other contemporary grammar theories, almost all the unification-based ones advocate the usage of a set of phrase structure rules to describe how acceptable utterances are formed in a particular language. The constituents of the rules are annotated with a set of features. Rules may be applied to phrases only if the structure of a rule and a phrase match each other, or in other words, if they unify. That is, if their features only take on values of the same types and within the same ranges. The thesis describes the implementation of a large-scale unification-based grammar for Swedish. Part of the text is devoted to the more theoretical and linguistic sides, discussing all the different grammar rules, while concentrating the main effort on the treatment of verb phrases. Another part addresses a range of different application areas in which a language processing system eq...