Inheritance-based models of the lexicon

A rapid and remarkable development took place within computational linguistics in the years immediately following the introduction of unification-based models of language, in particular Lexical Functional Grammar (LFG) and Generalized Phrase Structure Grammar (GPSG), which employ feature structures to represent linguistic information. By the end of the 1980s a consensus had emerged, according to which the lexicon, which pairs word forms with feature structures, constitutes the main repository of information in a language. Furthermore, hierarchical structuring had come to be viewed as an essential aspect or perhaps even the most salient characteristic of the lexicon (cf. Briscoe et al. 1993). GPSG, as conceived in Gazdar & Pullum (1982) and even in Gazdar et al. (1985), still largely represents the older, dichotomous view of the lexicon. Here major aspects of linguistic structure were encoded in syntactic rules, many of which later came to be regarded as stating the possible complement structures of verbs, i.e. lexical information. Later developments in the treatment of subcategorization are only alluded to in a footnote (cf. Gazdar et al. 1985: 107). While the question “How is a classification imposed on the content of the lexicon by the system of features” is raised (p. 13), the answer of GPSG does not explicitly model the hierarchical inheritance relations inherent in lexical classifications. Rather, these relations are captured in logical feature co-occurrence restrictions (FCRs) and feature specification defaults (FSDs), the latter of which, prophetically, are nonmonotonic. From the start the lexicalist orientation was prominent in LFG (cf. Bresnan 1982, therein Kaplan & Bresnan 1982) and reached a peak in the radical lexicalism of Karttunen (1986), which uses the framework of categorial grammar to shift the entirety of linguistic description to the lexicon. The move toward the lexicalist view was independent of hierarchical modelling, which emerged in other work. In particular, Flickinger (1987) pioneered the explicit description of relations between English verb classes in terms of inheritance hierarchies. On a separate front,