Lexical Semantics: The Problem of Polysemy

Lexical Semantics: The Problem of Polysemy

Lexical Semantics: The Problem of Polysemy

Lexical Semantics: The Problem of Polysemy

Synopsis

Lexical ambiguity presents one of the most intractable problems for language processing studies and, not surprisingly, it is at the core of research in lexical semantics. Originally published as two special issues of the Journal of Semantics, this collection focuses on the problem of polysemy, from the point of view of practitioners of computational linguistics.

Excerpt

and derivational morphology. Many cases of conventional nominal metonymy, such as those introduced above, can be analysed in these terms.

In section 2 we describe the lexical representation language that we have developed to represent basic lexical entries and characterize systematic lexical processes. In section 3 we return to constructional polysemy and motivate a more detailed analysis of specialization as well as discussing broadening in this framework. In section 4 we discuss sense extension proper with respect to grinding, portioning and other types of nominal metonymy; we address the issues of the directionality of sense extensions, and their apparent ability to apply to phrases in some cases, and their productive yet highly conventionalized nature. In section 5 we consider cases of 'co-predication' (Pustejovsky 1994), where distinct senses are accessible for coordination and modification, and present an analysis of some cases of co-predication compatible with our accounts of constructional polysemy and sense extension. In common with other lexical processes, sense extension is semi-productive in that it is susceptible to blocking and sensitive to frequency effects; in section 6 we argue that these properties can be captured by adopting a probabilistic interpretation of lexical rules and utilizing probabilities in a natural fashion in language production and interpretation.

2 THE LEXICAL REPRESENTATION LANGUAGE

The language we will use to represent these classes of polysemous behaviour is the lexical representation language (LRL) developed for the ACQUILEX lexical knowledge base system (LKB). The LRL is a typed feature structure language (Carpenter 1992), augmented with defaults and lexical rules. Types are used to structure lexical entries, which are represented as feature structures (FS), and specify how they combine by means of grammar rules, or alternatively by constraints on phrasal types. The LRL could be used to implement a range of unification- and constraint-based approaches. The approach taken in this paper can be regarded (roughly) as combining an HPSG-like approach to syntax with Pustejovsky's notion of qualia structure.

Earlier versions of the LRL have been described in Copestake (1992, 1993a, b) and we will only provide a brief sketch of the formalism here. In this paper, however, we will make use of an improved notion of default unification, which is order-independent and allows for persistent defaults (Lascarides et al. (forthcoming), see section 2.2 below). Most previous definitions of default unification have assumed that it involves incorporating into a non-default FS all the consistent information from a default FS, making no distinction in the result between information which arose from the default and non-default structures. In our treatment, by contrast, information in FSs may be marked as default (or . . .

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