Dan Fass

Providing Machine Tractable Dictionary Tools

Machine readable dictionaries (Mrds) contain knowledge about language and the world essential for tasks in natural language processing (Nlp). However, this knowledge, collected and recorded by lexicographers for human readers, is not presented in a manner for Mrds to be used directly for Nlp tasks. What is badly needed are machine tractable dictionaries (Mtds): Mrds transformed into a format usable for Nlp. This paper discusses three different but related large-scale computational methods to transform Mrds into Mtds. The Mrd used is The Longman Dictionary of Contemporary English (Ldoce). The three methods differ in the amount of knowledge they start with and the kinds of knowledge they provide. All require some handcoding of initial information but are largely automatic. Method I, a statistical approach, uses the least handcoding. It generates “relatedness” networks for words in Ldoce and presents a method for doing partial word sense disambiguation. Method II employs the most handcoding because it develops and builds lexical entries for a very carefully controlled defining vocabulary of 2,000 word senses (1,000 words). The payoff is that the method will provide an Mtd containing highly structured semantic information. Method III requires the handcoding of a grammar and the semantic patterns used by its parser, but not the handcoding of any lexical material. This is because the method builds up lexical material from sources wholly within Ldoce. The information extracted is a set of sources of information, individually weak, but which can be combined to give a strong and determinate linguistic data base.

An Account of Coherence, Semantic Relations, Metonymy, and Lexical Ambiguity Resolution

Publisher Summary This chapter defines the relationship between the resolution of lexical ambiguity, semantic relations, and metonymy within an account of coherence. Coherence is the synergism of knowledge, where synergism is the interaction of two or more discrete agencies to achieve an effect of which none is individually capable. Semantic relations and metonymy are instances of coherence and coherence is also used in resolving lexical ambiguity. This account of coherence, semantic relations, metonymy and lexical ambiguity resolution is embodied in Collative Semantics (CS). The four components of CS are sense-frames, collation, semantic vectors, and screening. Sense-frames are the knowledge representation scheme and represent individual word-senses. Collation matches the sense-frames of two word-senses, finds any metonymies between the sense-frames of the word-senses, and also discriminates the semantic relations between the word-senses as a complex system of mappings between their sense-frames. Semantic vectors represent systems of mappings produced by collation and therefore the semantic relations are encoded in those mappings.

Machine tractable dictionaries as tools and resources for natural language processing

This paper discusses three different but related large-scale computational methods for the transformation of machine readable dictionaries (MRDs) into machine tractable dictionaries, i.e., MRDs converted into a format usable for natural language processing tasks. The MRD used is The Longman Dictionary of Contemporary English.

Adapting a synonym database to specific domains

This paper describes a method for adapting a general purpose synonym database, like WordNet, to a specific domain, where only a subset of the synonymy relations defined in the general database hold. The method adopts an eliminative approach, based on incrementally pruning the original database. The method is based on a preliminary manual pruning phase and an algorithm for automatically pruning the database. This method has been implemented and used for an Information Retrieval system in the aviation domain.

Metonymy and metaphor: what's the difference?

A computational approach to metonymy and metaphor is proposed that distinguishes between them, literalness, and anomaly. The approach supports Lakoff and Johnsons (1980) views that metonymy and metaphor are quite different phenomena, that in metonymy an entity stands for another, whereas in metaphor an entity is viewed as another.

Processing complex noun phrases in a natural language interface to a statistical database

Analysis of a corpus of queries to a statistical database has shown considerable variation in the location and order of modifiers in complex noun phrases. Nevertheless, restrictions can be defined on nominal modification because of certain correspondences between nominal modifiers and the role they fulfill in a statistical database, notably that the names of database tables and columns, and values of columns, are all determined by the modifiers. These restrictions are described. Incorporating these restrictions into Head-Driven Phrase Structure Grammar (HPSG) has caused us to examine the treatment of nominal modification in HPSG. A new treatment is proposed and an implementation within an HPSG based natural language front-end to a statistical database is described.

Collative Semantics

This paper introduces Collative Semantics (CS), a new domain-independent semantics for natural language processing (NLP) which addresses the problems of lexical ambiguity, metonymy, various semantic relations (conventional relations, redundant relations, contradictory relations, metaphorical relations and severely anomalous relations) and the introduction of new information. We explain the two techniques CS uses for matching together knowledge structures (KSs) and why semantic vectors, which record the results of such matches, are informative enough to tell apart semantic relations and be the basis for lexical disambiguation.

Time-Constrained Machine Translation

This paper defines the class of time-constrained applications: applications in which the user has limited time to process the system output. This class is differentiated from real-time systems, where it is production time rather than comprehension time that is constrained. Examples of time-constrained MT applications include the translation of multi-party dialogue and the translation of closed-captions. The constraints on comprehension time in such systems have significant implications for the systems objectives, its design, and its evaluation. In this paper we outline these challenges and discuss how they have been met in an English-Spanish MT system designed to translate the closed-captions used on television.

Lexical Semantic Constraints

In linguistics and natural language processing, language has been described and theorized about in terms of constraints. Given that lexical semantics is the study of the meaning (’semantics’) of words (‘lexical’), the constraints that are the most natural focus for lexical semantics research are constraints on the meanings of words, i.e., what one might call lexical semantic constraints. A number of lexical semantic constraints is investigated; selectional restrictions (also known as preferences), assertions, relevance, salience, and restrictions on the internal semantic structure of nouns and verbs. The challenge for lexical semantics is to understand how such constraints are organized and used.

Reasoning using inheritance from a mixture of knowledge and beliefs

Certain inadequacies of homogeneous inheritance systems have caused an interest in heterogeneous inheritance systems. Heterogeneous representations allow for mixing of ‘known’ relations (inherited through ‘strict’ links) and what is ‘believed’ (inherits through ‘defeasible’ links). However, few well-founded systems have been proposed and heterogeneous systems have been considered to be not yet well understood. This paper presents a theory and implementation of a heterogeneous inheritance system. The principles of the system are that (i) rules of composition allow paths to be considered as single links (effective relationships), and (ii) rules of comparison allow selection of those effective relationships which state the most definite, specific information. These rules are enumerated and discussed, then an implementation of the theory is shown. An example of the operation of the system is explained in detail. Related recent work is noted.