Controlling the Application of Lexical Rules

Controlling the application of lexical rules Ted Briscoe ejb@cl, cam. ac .uk Computer Laboratory, University of Cambridge Ann Copestake aac@csli, stanford, edu CSLI, Stanford University Abstract In this paper, we describe an item-familiarity account of the semi-productivity of morphological and lexical rules, and illustrate how it can be applied to practical issues which arise when building large scale lexical knowledge bases which utilize lexical rules. Our approach assumes that attested uses of derived words and senses are explicitly recorded, but that productive use of lexical rules is also possible, though controlled by probabilities associated with rule application. We discuss how the necessary probabilities and estimates of lexical rule productivity may be acquired from corpora. 1 Introduction Lexicalist linguistic theories, such as HPSG, LFG and categorial grammar, rely heavily on lexical rules. Recently, techniques have been described which address the efficiency issues that this raises for fully productive rules, such as inflectional rules and 'syntactic rules' (such as the HPSG com- plement extraction lexical rule). For example, Bouma & van Noord (1994) and Johnson & Dorre (1995) propose techniques for delayed evaluation of lexical rules so that they apply 'on demand' at parse time. Meurers ~ Minnen (1995) present a covariation approach, in which a finite-state ma- chine for the application of lexical rules is derived by computing possible follow relations between the set of rules and then pruned FSMs are associated with classes of actual lexical entries repre- senting the restricted set of rules which can apply to those entries. Finally, entries themselves are extended with information common to all their derived variants. These techniques achieve most of the advantages of lexicon expansion in the face of recursive rules and cyclic rule interactions which preclude a full off-line expansion. Although these treatments allow for the efficient use of productive lexical rules, they do not ad- dress the issue of semi-productivity of derivational morphological and sense extension rules, which causes considerable problems in construction of broad coverage lexical knowledge bases (LKBs) (see, for example, Climent and Mart/(1995), Pirelli et al., 1994). The standard formalization of lexical rules entails that derived entries will exist without exception for any basic entry which is compatible with the lexical rule input description. Formal accounts of some classes of exceptions, such as preemption by synonomy, have been developed (e.g. Briscoe et al, 1995), but these suffer from the disadvantage that detailed lexical semantic information must be available to detect po- tential synonyms. The search for a fully productive statement of verb alternations has led to an increasingly semantic perspective on such rules. Pinker (1989) argues that so-called broad seman- tic classes (e.g. creation or transfer verbs) provide necessary conditions for lexical rule application, but that narrow class lexical rules should be specified, breaking down such rules into a number of fully-productive subcases. But, in the attempt to define such subcases, Pinker is forced to make subtle and often unintuitive distinctions. Similarly, Levin (1992) delimits classes of verbs to which particular sets of alternations apply, but some …

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